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COLLEGE  OF  PHYSICIANS      " 
AND   SURGEONS 


Reference  Library 

Given  by 


AN  INTRODUCTION  TO  PHYSIOLOGY 


AN    INTRODUCTION 


TO 


PHYSIOLOGY 


BY 


WILLIAM   TOWNSEND   POETEE,  M.D. 

ASSOCIATE    PROFESSOR    OF    PHTSIOLOGT  IN    THE 
HARVARD   MEDICAL   SCHOOL 


THE    UNIVERSITY    PRESS 

Cambrftgr,  fflass. 

1906 


Copyright,  1906, 
By  W.  T.  Porter. 


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PKEFACE  TO  THE  SECOND  EDITION 

Concentration,  sequence,  and  election  are 
fruitful  principles  in  the  higher  education. 

In  1898  the  Committee  on  Medical  Education, 
appointed  by  the  Harvard  Faculty  of  Medicine, 
reported  in  favor  of  the  "  concentration  "  system 
urged  in  the  committee  by  the  author  in  com- 
mon with  Professor  W.  T.  Councilman.  By  this 
method,  the  first  half-year  in  the  Medical  School 
is  devoted  to  anatomy  and  histology,  the  second 
half-year  to  physiology  and  biological  chemistry, 
the  third  half-year  to  pathology  and  bacteriology, 
and  the  fourth,  fifth,  and  sixth  half-years  to 
practical  medicine  and  surgery.  Work  under 
the  new  svstem  began  in  the  collegiate  year  of 
1899-1900.  In  1904,  largely  through  the  influ- 
ence of  Professor  Bowditch,  the  seventh  and 
eighth  half-years  were  made  elective,  each  stu- 
dent choosing  for  himself  the  studies  best  suited 
to  his  needs. 

Concentration  provides  that  the  student  shall 
not  serve  two   masters,  but   shall  study  at  one 


vi  PREFACE    TO   THE    SECOND    EDITION 

time  only  one  principal  subject,  such  as  physi- 
ology or  pathology,  disciplines  that  do  not  yield 
readily  to  a  divided  mind.  Sequence  provides 
that  a  foundation  shall  be  laid  before  the  super- 
structure is  attempted.  Students  now  have  an 
acquaintance  with  anatomy  before  they  begin 
the  study  of  physiology.  Election  somewhat 
tardily  intrusts  to  university  men  rarely  less 
than  twenty -five  years  of  age  a  voice  in  the 
decision  of  their  nearest  affairs.  The  application 
of  these  principles  to  medical  teaching  has  un- 
doubtedly resulted  in  large  savings  of  time  and 
energy. 

The  economy  of  force  secured  by  concentra- 
tion and  sequence  has  been  highly  valuable, 
though  not  indispensable,  in  the  new  teaching  of 
physiology  introduced  by  the  author  in  Feb- 
ruary, 1900.  The  traditional  teaching  of  physi- 
ology consists  of  lectures  illustrated  by  occasional 
demonstrations  and,  in  some  instances,  by  experi- 
ments performed  by  the  students  themselves. 
The  new  method  is  fundamentally  opposite.  It 
consists  of  experiments  and  observations  by  the 
student  himself.  The  didactic  instruction,  com- 
prising lectures,  written  tests,  recitations,  confer- 
ences, and  the  writing  and  discussing  of  theses, 
follows  the  student's  experiments  and  considers 
them  in  relation  to  the  work  of  other  observers. 


PREFACE    TO    THE    SECOND    EDITION  Vll 

In  the  old  method,  the  stress  is  upon  the  di- 
dactic teaching.  In  the  new  there  is  no  less 
didactic  teaching,  but  the  stress  is  upon  observa- 
tion. The  old  method  insensibly  teaches  men  to 
rest  upon  authority,  but  the  new  directs  them 
to  nature. 

The  new  method  requires : 

1.  Printed  accounts  of  the  fundamental  experi- 
ments and  observations  in  physiology,  taken  from 
the  original  sources,  and  arranged  in  the  most 
instructive  sequence.  The  reference  to  the  origi- 
nal source  should  be  given  in  each  case. 

2.  Accessory  data  grouped  about  the  funda- 
mental experiments.  The  accessory  data  should 
also  be  taken  as  directly  as  possible  from  the 
original  sources,  and  the  reference  given  in  each 
case. 

3.  Apparatus  of  precision  designed  with  the 
utmost  simplicity  upon  lines  that  permit  its 
manufacture  in  large  quantities  at  small  cost. 

It  is  obvious  that  these  conditions  cannot  be 
met  without  prolonged  labor.  Meanwhile,  the 
annual  classes  in  physiology  must  be  taught. 
The  present  volume  is  a  collection  of  fundamen- 
tal and  accessory  experiments  in  several  fields 
printed  in  an  abbreviated  form  for  the  temporary 
use  of  Harvard  Medical  students  and  other  inter- 
ested persons.    This  collection  is  being  completed 


Vlii  PREFACE    TO   THE    SECOND   EDITION 

and  improved  as  rapidly  as  possible,  and  the  data 
for  the  remaining  fields  are  being  brought  to- 
gether. In  its  final  form  this  material  will  con- 
stitute  "  A  Laboratory  Text-book  of  Physiology." 

The  Harvard  Medical  School, 
January,  1906. 


CONTENTS 


PART   I 

THE  GENERAL   PROPERTIES  OF 
LIVING  TISSUES 

I 

Page 

Introduction 3 

Nerve-muscle    preparation  —  Preliminary    considerations 
regarding  energy,  stimulation,  and  irritability. 

II 

Methods  of  Electrical  Stimulation 

Introduction 12 

Kinetic  theory  —  Osmotic  pressure  —  Plasmolysis.  Isotony 
—  Estimation  of  osmotic  pressure  in  the  blood  serum  — 
Surface  tension  —  Electrolysis  —  Electrolytic    solution 
pressure. 

The  Electrometer,  the  Rheochord,  and  the  Cell       34 
Surface  tension  altered  by  electrical  energy  —  Electrom- 
meter  —  Rheochord  —  Long    rheochord  —  Square  rheo- 
chord —  Simple  key  —  Short-circuiting  key  —  Polariza- 
tion —  Pole-changer  —  Polarization  current  —  Dry  cell. 

Induction  Currents 53 

Inductorium  —  Magnetic  induction  —  Magnetic  field. 
Lines  of  force  —  To  produce  electric  induction,  lines 
of  magnetic  force  must  be  cut  by  circuit  —  Electro- 
magnetic induction  —  On  the  construction  of  the  induc- 
torium —  Empirical  graduation  of  inductorium  —  Plat- 
inum  electrodes  —  Flat-jawed   clamp  —  Round-jawed 


X  CONTENTS 

Page 
clamp  —  Double  clamp  —  Make   and  break   induction 
currents  as  stimuli  —  Extra   currents  at  opening  and 
closing  of  primary  current  —  Tetanizing  currents  —  In- 
duction in  nerves  —  Exclusion  of  make  or  break  current. 

Unipolar  Induction 71 

in 

The  Graphic  Method 

The  Graphic  Method 77 

Kymograph  —  Long  paper  kymograph  —  Light  muscle 
lever  —  Writing  lever  —  Tuning  fork. 

The  Electrical  Stimulation  oe  Muscle  and  Nerve 

The  Galvanic  Current 93 

Non-polarizable  electrodes  —  Moist  chamber  —  Destruc- 
tion of  the  brain  by  pithing  —  Paralysis  of  voluntary 
motion  by  curare  —  Opening  and  closing  contraction 
—  Changes  in  intensity  of  stimulus. 

Polar  Stimulation  of  Muscle 101 

Ureter  —  Gaskell  Clamp  —  Intestine  —  Electro-magnetic 
signal — Tonic  contraction  —  Physiological  anode  and 
cathode  —  Polar  stimulation  in  heart. 

Polar  Stimulation  of  Nerve 113 

Law  of  contraction  —  Changes  in  irritability —  Changes  in 
conductivity. 

Stimulation  of  Human  Nerves 127 

Stimulation  of  motor  points  —  Polar  stimulation  of  human 
nerves  —  Brass  electrodes  —  Reaction  of  degeneration. 

Galvanotropism 137 

Paramecium. 

Influence  of  Duration  of  Stimulus 138 

Tonic  contraction  —  Rhythmic  contraction  —  Continuous 
galvanic  stimulation  of  nerve  may  cause  periodic  dis- 


CONTENTS  XI 

Page 
charge  of  nerve  impulses  —  Polarization  current  —  Polar 
fatigue  —  Opening  and  closing  tetanus  —  Polar  excitation 
in  injured  muscle. 
Polar  Inhibition  by  the  Galvanic  Current  .     .     .     153 

Heart  —  Polar  inhibition  in  veratrinized  muscle. 
Stimulation  affected  by  the  Form  of  the  Muscle     156 
Effect  of  the  Angle  at  which  the  Current  Line* 

cut  the  Muscle  Fibres 157 

The  Induced  Current 158 


Chemical  and  Mechanical  Stimulation 

Chemical  Stimulation 163 

Effect  of  distilled  water  —  Strong  saline  solutions  —  Dry- 
ing—  "Normal  saline"  —  Importance  of  calcium  — 
Constant  chemical  stimulation  may  cause  periodic 
contraction. 

Mechanical  Stimulation 166 

Idio-niuscolar  contraction/ 


VI 

Irritability  and  Conductivity 

Irritability  and  Conductivity 168 

Independent  irritability  of  muscle  —  Irritability  and  con- 
ductivity are  separate  properties  of  nerve  —  Minimal  and 
maximal  stimuli;  threshold  value  —  Summation  of  in- 
adequate single  stimuli  —  Relative  excitability  of  flexor 
and  extensor  nerve  fibres  ;  Ritter-Rollett  phenomenon  — 
Specific  irritability  of  nerve  greater  than  that  of  muscle  — 
Irritability  at  different  points  of  same  nerve  —  Excitation 
wave  remains  in  muscle  or  nerve  fibre  in  which  it  starts 
—  Same  nerve  fibre  may  conduct  impulses  both  centrip- 
etally  and  centrifugally  —  Speed  of  nerve  impulse. 


XU  CONTENTS 


PAET   II 
THE  INCOME  OF  ENERGY 

I 

Fermentation 

Page 

Hydrolysis  of  Starch  by  Diastase 189 

Conversion  of  starch  to  sugar  by  germinating  barley  —  Con- 
version of  starch  to  sugar  by  salivary  diastase  (ptyalin)  — 
Extraction  of  diastase  from  germinating  barley  —  Specific 
action  of  ferments. 

Proteid  Digestion  by  Pepsin 192 

Gastric  digestion  of  cooked  beef  and  bread  —  Artificial 
gastric  juice  —  Digestion  with  artificial  gastric  juice  — 
Extraction  of  pepsin  —  Change  of  proteid  to  peptone  by 
pepsin. 

Splitting  of  Casein  by  Rennin 195 

Rennin  extract — Separation  of  rennin  —  Precipitation  of 
casein  —  Experiments  of  Arthus  and  Pages. 

Precipitation  of  Fibrin  by  Fibrin  Ferment  .     .     .     199 
Buchanan's  experiment  —  Extraction  of  fibrin  ferment  — 
Extraction  of  fibrinogen  —  Precipitation  of  fibrinogen  by 
fibrin  ferment. 

Ammonia*  a i.  Fermentation  of  Urea  by  Urease.     .     201 
Extraction  of  urease. 

Splitting  and  Synthesis  of  Fats 205 

Chemistry  of  fats  and  soups  —  Splitting  of  fats  by  the  pan- 
creatic juice  —  Preparation  of  neutral  fat  —  The  emulsion 
tesl  lor  fatty  acid — Extraction  of  lipase  —  Hydrolysis 
of  ethyl  butyrate  by  lipase  —  Synthesis  of  neutral  fat 
by  lipase. 


V 


CONTENTS  Xlll 

Page 

Immunity 218 

Ehrlich's  ricin  experiments  —  Ricin  antitoxine  —  Theory 
of  immunity. 
Haemolytic  and  Bacteriolytic  Ferments  ....     227 
Bordet's  experiments. 

Oxidizing  Ferments 230 

Schonbein's  experiment  —  Farther  oxidations  by  animal 
tissues  —  Oxidation  by  nucleo-proteid  —  Oxidation  about 
the  nucleus  —  Glycolysis  in  blood  —  Oxidation  not  de- 
pendent on  living  cells  of  blood  —  Relation  of  glycolysis 
to  the  pancreas  and  the  lymph  —  Glycolytic  ferment  of 
pancreas. 

Alcoholic  Fermentation 238 

The  yeast  plant  —  Chemical  relations  of  carbohydrates. 

Activating  Ferments 243 

Enterokinase  —  Conversion  of  trypsinogen  to  trypsin  by 
-  enterokinase. 

Absorption  of  Proteids 245 

Diffusion  of  proteids  through  dead  membrane  —  Diffusion 
through  living  intestinal  wall  —  Absorption  velocity  com- 
pared with  diffusion  velocity  —  Assimilable  proteids  — 
Non-assimilable  proteids — Alimentary  albuminuria  — 
Albumose  and  peptone  not  ordinarily  present  in  the 
blood  or  urine  —  Albumose  and  peptone  changed  in  their 
passage  through  the  intestinal  wall. 

Absorption  of  Fats,  Fat  Acids,  and  Soaps    .     .     .     259 
Absorption  of  fat  —  Absorption  of  fat  acids  —  Absorption 
of  fat  acid  as  a  soap. 

Lymph 262 

Permeability  of  vessel  wall  in  inflammation. 

II 
Blood 

Specific  Gravity 264 

Drawing  the  blood  —  Determination  of  specific  gravity. 

Counting  the  Corpuscles 266 

Counting  the  red  corpuscles  —  Counting  the  white  cor- 
puscles. 


XIV  CONTENTS 

Page 
Estimation  of  Haemoglobin 269 

Oxygen  capacity  of  the  blood  ;  the  colorimetric  determina- 
tion of  haemoglobin. 

Haemorrhage  and  Regeneration 273 

Physical  Aspects  of  Coagulation 273 

Physical  action  of  salts  in  the  coagulation  of  colloidal 
mixtures  —  Physical  changes  in  coagulation. 

Secretion 276 

Speed  of  absorption  and  secretion. 

Ill 

Respiration 

Chemistry  of  Respiration 277 

Estimation  of  oxygen,  carbon  dioxide,  and  water. 

Metabolism 278 

Effect  of  muscular  exercise  on  the  oxygen,  carbon  dioxide, 
and  water  of  the  respired  air  —  Individual  level  of  pro- 
teid  metabolism  —  Nitrogenous  equilibrium  —  Effect  of 
muscular  exercise  on  proteid  metabolism. 


PAET   III 

THE   OUTGO   OF  ENERGY 

I 
Animal  Heat 

Animal  Heat 285 

Regional  temperature  —  Effect  of  hot  and  cold  drinks  on 
the  temperature  of  the  mouth  — Hourly  variation —  Re- 
action of  cold  and  warm  blooded  animals  to  changes  in 
the  external  temperature  —  Chemical  action  the  source 
of  animal  heat. 


CONTENTS  XV 


n 

The  Electromotive  Phenomena  of  Muscle  and 
Nerve 

Page 

The  Demarcation  Current  of  Muscle 287 

Demarcation  current  of  muscle  —  Stimulation  by  demarca- 
tion current  —  Interference  between  demarcation  current 
and  stimulating  current ;  polar  refusal. 

Demarcation  Current  of  Nerve 295 

Nerve  may  be  stimulated  by  its  own  demarcation  current. 

Hypotheses  regarding  the  Causation  of  the  De- 
marcation Current 297 

Action  Current  of  Muscle 302 

Rheoscopic  frog  —  Action  current  in  tetanus;  stroboscopic 
me.thod  —  Action  current  of  human  muscle  —  Action 
current  of  heart. 

Action  Current  of  Nerve 315 

Negative  variation  —  Positive  variation  —  Positive  after 
current  —  Contraction  secured  with  a  weaker  stimulus 
than  negative  variation  —  Current  of  action  in  optic 
nerve  —  Errors  from,  unipolar  stimulation. 

Secretion  Current 320 

Secretion  current  from  mucous  membrane  — -  Negative  vari- 
ation of  secretion  current. 

Electrotonic  Currents 323 

Negative  variation  of  electrotonic.  currents  ;  positive  vari- 
ation (polarization  increment)  of  polarizing  current 
—  Electrotonic  current  as  stimulus. 

Electric  Fish 329 


XVI  CONTENTS 

III 

The  Change  in  Form 

Page 

Volume  of  Contracting  Muscle 331 

The  Single  Contraction  or  Twitch 332 

Muscle  curve  —  Duration  of  the  several  periods  —  Exci- 
tation wave  —  Contraction  wave  —  Relation  of  strength 
of  stimulus  to  form  of  contraction  wave  —  Influence  of 
load  on  height  of  contraction  — Influence  of  temperature 
on  form  of  contraction  —  Muscle  warmer  —  Influence  of 
veratrine  on  form  of  contraction. 

Tetanus 346 

Superposition  of  two  contractions  —  Superposition  in  teta- 
nus —  Relation  of  shortening  in  a  single  contraction  to 
shortening  in  tetanus. 

The  Isometric  Method 349 

Graduation  of  isometric  spring  —  Heavy  muscle  lever  — 
Isometric  contraction. 

Contraction  of  Human  Muscle 353 

Simple  contraction  or  twitch  —  Ergograph  —  Isometric 
contraction  —  Artificial  tetanus  —  Natural  tetanus. 

Smooth  Muscle 356 

Spontaneous  contractions  —  Simple  contraction  —  Tetanus. 
The  Work  Done 358 

Influence  of  load  on  work  done  —  Absolute  force  of  mus- 
cle —  Total  work  done  ;  the  work  adder  —  Total  work 
done  estimated  by  muscle  curve — Time  relations  of 
developing  energy. 

Elasticity  and  Extensibility 363 

Elasticity  and  extensibility  of  a  metal  spring  —  Of  a  rubber 
band  —  Of  skeletal  muscle  —  Extensibility  increased  in 
tetanus. 

Fatigue 366 

Skeletal  muscle  of  frog  —  Human  skeletal  muscle 


CONTENTS  XVll 

IV 

The  Central  Nervous  System 

Page 

Simple  Reflex  Actions 370 

The  spinal  cord  a  seat  of  simple  reflexes  —  Influence  of 
afferent  impulses  on  reflex  action  —  Threshold  value 
lower  in  end  organ  than  in  nerve-trunk — Summation 
of  afferent  impulses  —  Segmental  arrangement  of  reflex 
apparatus  —  Reflexes  in  man. 

Tendon  Reflexes 375 

Knee  jerk  —  Ankle  jerk  —  Gower's  experiment. 

Effect  of  Strychnine  on  Reflex  Action  ....     377 

Complex  Co-ordinated  Reflexes 377 

Removal  of  cerebral  hemispheres  —  Posture,  etc.  —  Bal- 
ancing experiment—  Retinal  reflex —  Croak  reflex. 

Apparent  Purpose  in  Reflex  Action 381 

Reflex  and  Reaction  Time 382 

Reflex  time —  Reaction  time  —  Reaction  time  with  choice. 

Inhibition  of  Reflexes 384 

Through  peripheral  afferent  nerves  —  Through  central 
afferent  paths;  the  optic  lobes. 

The  Roots  of  Spinal  Nerves 386 

Ludwig's  demonstration  —  Localization  of  movements  at 
different  levels  of  the  spinal  cord. 

Distribution  of  Sensory  Spinal  Nerves    ....     388 

Muscular  Tonus 389 

Brondgeest's  experiment. 

V 

The  Skin 

Sensations  of  Temperature 390 

Hot  and  cold  spots — Outline  —  Mechanical  stimulation 
—  Chemical  stimulation  —  Electrical  stimulation  — Tem- 
perature after-sensation —  Balance  between  loss  and  gain 


XVU1  CONTENTS 


of  heat  —  Fatigue  —  Relation  of  stimulated  area  to  sen 
sation  —  Perception  of  difference — Relatively  insensitive 
regions. 

Sensations  of  Pressure 393 

Pressure  spots  —  Threshold  value  —  Touch  discrimina- 
tion —  Weber's  law  —  After-sensation  of  pressure  — 
Temperature  and  pressure  —  Touch  illusion ;  Aristotle's 
experiment. 

VI 
General  Sensations 

Tickle 398 

Irradiation  —  After  image  —  Topography  —  Summation  — 
Fatigue. 

Pain 399 

Threshold  value  —  Latent  period  —  Summation  —  Topog- 
raphy—  Individual  variation — Temperature  stimuli. 

Motor  Sensations 400 

Judgment  of  weight  —  Sensation  of  effort  —  Sensation  of 
motion. 

VII 
Taste 

Taste 401 

Threshold  value  —  Topography  —  Relation  of  taste  to  area 
stimulated  —  Electrical  stimulation. 


VIII 

Introduction  to  Physiological  Optics 

Reflection  from  Plane  Mirrors 403 

Angles  of  incidence  and  reflection. 

Reflection  prom  Concave  Mirrors 405 

Principal  focus  —  Conjugate  foci  — Virtual  image  —  Con- 
struction of  image  from  concave  mirrors. 


CONTEXTS  xix 

Page 

Reflection  from  Convex  Mirrors 410 

Refraction 410 

Refraction  by  Prisms 413 

Construction  of  the  path  of  a  ray  passing  through  a  prism. 

Refraction  by  Convex  Lenses 416 

Principal  focus — Estimation  of  principal  focal  distance  — 
Conjugate  foci  —  Virtual  image  —  Construction  of  image 
obtained  with  convex  lens. 

Refraction  by  Concave  Lenses 422 

Refraction  by  Segments  of  Cylinders 422 

Refraction  through   Combined   Convex  and  Cylin- 
drical Lenses 424 

Aberration 426 

Spherical  aberration  by  reflection  —  Spherical  aberration 
by  refraction  —  Dispersion  circles  —  Myopia  —  Hyper- 
metropia  —  Chromatic  aberration  — Aberration  avoided 
by  a  diaphragm, 

Numbering  of  Prisms  and  Lenses 435 

Numbering  of  prisms  —  Numbering  of  lenses. 

IX 

Refraction  in  the  Eye 

Refraction  in  the  Eye 437 

The  eye  as  a  camera  obscura. 

The  Schematic  Eye 438 

Cardinal  Points  of  the  Cornea  (System  A)  .     .     .     440 
Construction  drawing  of  System  A  —  Principal  focal  dis- 
tances —  Construction  of  image  —  Calculation  of  position 
to  conjugate  foci. 

Cardinal  Points  of  the  Crystalline  Lens  (System  B)    445 
Construction  drawing  of  System  B  — Optical  centre —  Nodal 
points  —  Principal   surfaces  —  The   point  s  —  Principal 
points  —  Principal  focal  distances. 

Cardinal  Points  of  the  Eye  (System  C)    .     .     .     .     451 
Principal  surfaces  —  Nodal  points  —  Principal  foci. 


XX  CONTENTS 

Page 
Calculation  of  the  Situation  and  Size  of  Dioptric 

Images 456 

Reduced  Eye 458 

Relations  of  the  Visual  Axis 463 

Visual  angle  —  Apparent  size — Size  of  retinal  image  — 
Acuteness  of  vision  —  Smallest  perceptible  image  — 
Measurement  of  visual  acuteness. 

Accommodation 469 

Schemer's  experiment  — Dispersion  circles  —  Diameter 
of  circles  of  dispersion — Accommodation  line. 

Mechanism  of  Accommodation 473 

Narrowing  of  pupil  —  Relation  of  iris  to  lens  —  Changes 
in  the  lens. 

Measurement  of  Accommodation 479 

Far  point  —  Determination  of  far  point — Near  point  — 
Determination  of  near  point —  Range  of  accommodation. 

Ophthalmoscopy 484 

Reflection  from  retina — Influence  of  angle  between  light 
and  visual  axis  —  Influence  of  size  of  pupil  —  Influence 
of  nearness  to  pupil  —  Ophthalmoscope. 

Direct  Method 490 

Emmetropia  —  Ametropia  ;     qualitative   determination  — 

Measurement  of  myopia  —  Measurement  of  hypermetro- 

pia — Measurement  of  astigmatism. 
Indirect  Method 496 


Vision 

Viston 499 

Mapping  the  blind  spot  —  Yellow  spot  —  Field  of  vision. 

Color  Blindness 501 

Method  of  examination  and  diagnosis. 


CONTENTS  XXI 

XI 

Mechanics  of  Respiration 

Page 

Mechanics  of  Respiration 505 

Artificial  scheme  —  Inspiration  —  Expiration  —  Normal 
respiration  —  Forced  respiration  —  Obstructed  air  pas- 
sages —  Asphyxia  —  Coughing ;  sneezing  —  Hiccough  — 
Perforation  of  the  pleura. 

XII 

The  Circulation  of  the  Blood 

The  Mechanics  of  the  Circulation 508 

Circulation  scheme. 
The  Conversion  of  the   Intermittent  into  a  Con- 
tinuous Flow 515 

The  Relation  between  Rate  of  Flow  and  Width 

of  Bed 519 

The  Blood-Pressure 521 

Relation  of  peripheral  resistance  to  blood-pressure  — 
Curve  of  arterial  pressure  in  the  frog  —  Effect  on  blood- 
pressure  of  increasing  tbe  peripheral  resistance  in  the 
frog  —  Changes  in  the  stroke  of  the  pump;  inhibition 
of  the  ventricle  —  Effect  of  inhibition  of  the  heart  on 
the  blood-pressure  in  the  frog. 

The  Heart  as  a  Pump 525 

Opening  and  closing  of  the  valves  —  Period  of  outflow 
from  the  ventricle  —  Sphygmograph  tambour  — Visible 
change  in  form  —  Graphic  record  of  ventricular  contrac- 
tion. 

The  Heart  Muscle 530 

All  contractions  maximal  —  Staircase  contractions  —  Iso- 
lated apex ;  Bernstein's  experiment  —  Rhythmic  con- 
tractility of  heart  muscle  —  Constant  stimulus  may  cause 
periodic  contraction  —  Inactive  heart  muscle  still  irri- 
table—  Refractory  period;  extra-contraction;  compen- 
satory pause — Transmission  of  the  contraction  wave 
in  the  ventricle ;  Engelinann's  incisions  —  Transmission 


xxii  CONTENTS 

Page 
of  the  cardiac  excitation  from  auricle  to  ventricle; 
GaskeU's  block — Tonus  —  Influence  of  "load"  on  ven- 
tricular contraction  —  Influence  of  temperature  on  fre- 
quency of  contraction  —  Action  of  inorganic  salts  on 
heart  muscle. 

The  Heart  Sounds 541 

The  Pressure-Pulse 543 

Frequency  —  Hardness  —  Form  —  Volume  —  Pressure- 
pulse  in  the  artificial  scheme  —  Human  pressure-pulse 
curve  —  Low  tension  pressure-pulse  —  Pressure-pulse 
in  aortic  regurgitation — Stenosis  of  the  aortic  valve 
— Incompetence  of  the  mitral  valve. 

The  Volume  Pulse 552 

XIII 

The  Innervation  of  the  Heart  and  Blood-Vessels 

The  Innervation  of  the  Heart  and  Blood- Vessels  554 

The  Augmentor  Nerves  of  the  Heart 555 

Preparation  of  the  sympathetic  —  Action  of  sympathetic 
on  heart. 

The  Inhibitory  Nerves  of  the  Heart 558 

Preparation  of  the  vagus  nerve  —  Stimulation  of  cardiac 
inhibitory  fibres  in  vagus  trunk  —  Effect  of  vagus 
stimulation  on  the  auriculo-ventricular  contraction  in- 
terval — Irritability  of  the  inhibited  heart  —  Intracar- 
diac inhibitory  mechanism  —  Inhibition  by  Stannius 
ligature  —  Action  of  nicotine  — Atropine  —  Muscarine 
—  Antagonistic  action  of  muscarine  and  atropine. 

The  Centres  of  the  Heart  Nerves       564 

Inhibitory  centre  —  Augmentor  centre —  Reflex  inhibition 
of  the  heart ;  Goltz's  experiment  —  Reflex  augmentation. 

The  Innervation  of  the  Blood-Vessels  ....  568 
Bulbar  centre — Vasomotor  functions  of  the  spinal  cord  — 
Effect  of  destruction  of  the  spinal  cord  on  the  distri- 
bution of  the  blood  —  Vasomotor  fibres  leave  the  cord 
in  the  anterior  roots  of  spinal  nerves  —  Vasoconstrictor 
fibres  in  the  sciatic  nerve —  Vasodilator  nerves —  Reflex 
vasomotor  actions. 


ft 

ILLUSTRATIONS 

Diagrams  which  merely  illustrate  the  grouping  of  apparatus  for  a  par- 
ticular experiment  are  omitted  from  this  list. 

Fig.  Page 

1.  Muscles  of  left  hind  limb  of  frog,  dorsal  view       .     .  6 

2.  Nerve-muscle  preparation 7 

3.  Muscle  clamp,  stand,  and  nerve-holder       ....  8 

4.  Tension  indicator 25 

5.  Stage  electrometer 38 

6.  Long  rheochord 43 

7.  Square  rheochord 44 

8.  Simple  key 45 

9.  Short-circuiting  key 46 

11.  Pole-changer,  early  form 49 

12.  Rocking  key 50 

14.  Inductorium 54 

15.  Platinum  electrodes 65 

16.  Flat-jawed  clamp  and  round-jawed  clamp  ....  66 

17.  Double  clamp 66 

19.  Long  paper  kymograph 82 

20.  Smoker 84 

21.  Light  muscle  lever 86 

22.  Tuning  fork 87 

23.  ISTon-polarizable  electrodes 94 

24.  Moist  chamber 95 

25.  Hind  limb  of  frog,  anterior  view 99 

25.  Gaskell  clamp 103 

26.  Electro-magnetic  signal 105 

28.  Frog  board 112 


XXIV  ILLUSTRATIONS 

Fig.  Page 

35.  Motor  points  on  the  anterior  surface  of  the  forearm 

and  hand 128 

36.  Motor  points  on  the  posterior  surface  of  the  forearm  129 

and  hand 

38.  Brass  electrodes 132 

42.  Gas    chamber,    with    bottle   for   generating    curbon 

dioxide 172 

43.  Sartorius 181 

44.  Gracilis 183 

48.  Scheme  of  myomeres  in  a  parallel-fibred  muscle  .     .  298 

49.  Scheme  of  myomeres  in  an  oblique  section       .     .     .  299 

50.  Vibrating  interrupter 303 

51.  Vibrating  interrupter  arranged  to  make  one  contact 

per  second 304 

53.  Heart  lever 311 

54.  Scheme  of  differential  rheotome 313 

58.  Volume  tube 332 

59.  Muscle  warmer 343 

60.  Heavy  muscle  lever 351 

61.  Ergograph 354 

62.  Work  adder 359 

63.  Lantern  and  optical  box 404 

65.  Reduced  eye 459 

67.  Respiration  scheme 504 

68.  Quantitative  circulation  scheme 512 

69.  Mercury  manometer 523 

70.  Sphygmograph 527 

71.  Sphygmograph  tambour 528 

72.  Scheme  of  sympathetic  nerve  in  frog 556 

73.  Scheme  of  cervical  nerves  in  frog 558 

74.  View  of  brain  of  frog  from  above 565 


PART   I 

THE   GENERAL   PROPERTIES    OF   LIVING 
TISSUES 


PART    I 

THE   GENERAL   PROPERTIES    OF 
LIVING   TISSUES 


INTRODUCTION 

Until  recent  times  it  was  believed  that  many  of 
the  compounds  found  in  the  tissues  of  animals 
and  plants  could  be  made  only  by  the  action  of 
organized,  i.  e.  living  matter.  Such  compounds 
were  called  organic  to  distinguish  them  from 
those  found  in  inorganic  or  inanimate  nature. 
The  forces  producing  organic  compounds  were 
thought  to  be  partly  the  ordinary  chemical 
and  physical  processes  known  to  science,  and 
partly  certain  mystical  agencies  termed  vital 
forces.  The  great  discovery  of  Wohler  in 
1828  that  urea  (C02NH2),  a  typical  organic 
compound,  could  be  made  synthetically  in  the 
laboratory,  overthrew  this  conception  and  was 
the  beginning  of  a  long  and  fruitful  struggle  to 


4        GENERAL    PROPERTIES    OF   LIVING   TISSUES 

bring  the  phenomena  of  living  matter  within 
the  operation  of  chemical  and  physical  laws 
without  recourse  to  the  supernatural  and  occult. 
According  to  this  new,  unified  view  of  nature, 
which  is  the  foundation  of  modern  physiology, 
all  phenomena,  whether  animate  or  inanimate, 
are  alike  the  expression  of  chemical  and  physi- 
cal processes,  some  known,  some  unknown,  none 
of  which  is  fundamentally  different  from  the 
rest. 

The  physiologist,  therefore,  now  looks  upon 
the  reactions  of  living  matter  with  the  eye  of 
the  physicist,  and  it  is  of  the  first  importance 
to  beginners  in  physiology  to  acquire  this  point 
of  view.  To  this  end  it  is  desirable  to  consider 
living  tissues  from  the  standpoint  of  energy  and 
to  divide,  even  imperfectly,  the  functions  to  be 
studied  into  those  that  have  to  do  with  the 
income  of  energy  and  those  that  are  active  in 
its  outgo.  These  studies  cannot,  however,  be 
profitably  undertaken  without  some  acquaint- 
ance with  the  general  properties  of  living  tissues, 
such  as  irritability  and  contractility. 

We  shall  begin,  therefore,  by  examining  a 
motor  nerve  and  the  muscle  in  which  its  fibres 
are  distributed. 

The  Nerve-Muscle  Preparation.  —  Wrap  the 
frog  in  the  cloth,  the  head  out.     Pass  one  blade 


INTRODUCTION  5 

of  the  stout  scissors  between  the  jaws.  Bring 
this  blade  to  the  angle  of  the  jaw,  the  other 
blade  over  the  junction  of  the  head  and  trunk. 
Cut  off  the  skull  with  a  single  closure  of  the 
scissors.  Thrust  the  pithing  wire  into  the  cranial 
cavity  and  then  into  the  vertebral  canal,  destroy- 
ing the  brain  and  spinal  cord.  The  frog  ceases 
to  move;  the  muscles  are  relaxed.  Divide  the 
body  transversely  behind  the  fore  limbs.  Ee- 
move  the  viscera.  Seize  the  spinal  column  with 
the  finger  and  thumb  of  one  hand,  and  the 
skin  of  the  back  with  the  other  hand,  covered 
with  a  cloth  to  prevent  slipping.  Draw  the 
hind  limbs  out  of  the  skin.  Lay  the  limbs 
down,  back  uppermost,  upon  a  clean  glass 
plate,  which  the  outside  of  the  frog's  skin  has 
not  touched.  The  skin  of  the  frog,  like  that  of 
the  salamander  and  some  other  batrachians,  is 
provided  with  a  protective  secretion  injurious  to 
sensitive  tissues.  Note  on  the  outside  of  the 
thigh  the  triceps  femoris  muscle ;  on  the  median 
side,  the  semi-membranosus ;  between  these,  the 
narrow  biceps  femoris.  (Fig.  1.)  Cautiously  di- 
vide the  connective  tissue  between  the  semi- 
membranosus and  the  biceps  femoris.  On 
drawing  these  muscles  apart,  the  sciatic  nerve 
and  the  femoral  vessels  will  be  seen.  Clear  the 
nerve  with  scissors  and   forceps  from   the  knee 


GENERAL   PROPERTIES   OF   LIVING   TISSUES 


to  the  vertebral  column.  The  nerve  itself  should 
not  be  touched  with  the  instruments.  Near  the 
pelvis  it  will  be  necessary  to  divide  the  pyriform 
and  the  iliococcygeal  muscles:    carefully  avoid 

the   nerve   while    do- 
ing this. 

With  the  forceps 
lift  the  tip  of  the 
urostyle  (the  10th 
vertebra,  a  long,  slen- 
der bone  which  forms 
the  caudal  end  of  the 
vertebral  column) 
and  remove  the  bone 
with  the  stout  scissors 
as  far  as  the  9th 
vertebra.  Divide  the 
spinal  column  trans- 
versely between  the 
Fig.  i.  Muscles  of  left  hind  limb  of  6th  an(^  'th  vertebrae. 

frog,  <lorsal  view  (Ecker  and  Wieders-  Tiivyi  the  ffO0"  back 
heim ).  ° 

down.  Bisect  length- 
wise the  7th,  8th,  and  9th  vertebras.  Grasp 
the  half  from  which  the  prepared  nerve  springs 
and  lift  it  gently,  freeing  the  nerve  with  the 
scissors  down  to  the  knee. 

Puss  now  to  the  leg.     Cut  through  the  Achil- 
les  tendon   of   the  gastrocnemius  muscle  below 


INTRODUCTION 


the  thickening  at  the  heel.     Free  the  muscle  up 

to  its  origin  from  the  femur,  taking  care  not  to 

harm  the  branch  of  the  nerve  which  enters  the 

muscle   on  its  posterior  surface  near  the  knee. 

Cut  through  the  tibia  about  one 

centimetre  from  the  knee-joint. 

Clear  away  the    muscles  of  the 

thi^h  from  the  lower  end  of  the 

femur,  avoiding  the  sciatic  nerve. 

Cut   through    the    femur   about 

its  middle.     (Fig.  2.)     Lay  the 

sciatic  nerve  for  safety  along  the 

gastrocnemius   muscle.      Fasten 

the  lower  fragment  of  the  femur     Fi°- 2-  Nerve-mus- 

cle  preparation;  gas- 
in    the  jaWS  Of  the  mUSCle  Clamp,    trocnemius     muscle 

cinil  scititic  nerve    F 

Let  the  whole  nerve  rest  with-  end  of  femur  jn.'sci- 
out  stretching  on  the  adjustable  l?ha™aS- 
plate  or  nerve-holder,  the  filter  meat  of  smaller  ten- 

don  of  gastrocnemius 

paper    Covering    Which    Should  be    to  femur  (Handbook 

,  .    ,  ,  , .  for  the  Physiological 

moistened   with    normal    saline  Laboratory). 
solution    (0.6    per   cent    NaCl). 
Take  care  that  the  nerve  does  not  dry  between 
the  nerve-holder  and  the  muscle.     (Fig.  3.)    The 
filter  paper  should  reach  from  the  nerve-holder 
to  the  muscle. 

Preliminary  Considerations  regarding  Energy, 
Stimulation,  and  Irritability.  —  Pinch  the  muscle 
sharply  with  the  forceps. 


8        GENERAL   PROPERTIES   OF   LIVING   TISSUES 

The   muscle  passes   into   the   active  state;   it 
shortens  and  thickens.     The  foot,  which  is  rela- 


Fig.  3.  The  muscle  clamp,  stand,  and  nerve-holder.  The  nerve-holder 
supports  the  sciatic  nerve,  together  with  the  portion  of  the  spinal  column 
from  which  it  springs.  The  handle  of  the  nerve-holder  is  of  thick  lead 
wire  which  may  be  bent  as  desired.  The  binding  post  on  the  muscle  clamp 
provides  electrical  connection  with  the  upper  end  of  the  muscle. 

tively  less  fixed  than  the  leg,  is  extended.  The 
contraction  is  followed  by  a  slower  relaxation  or 
return  to  the  original  form. 


INTRODUCTION  9 

Observe  that  the  mechanical  act  of  pinching 
caused  the  resting  muscle  to  become  active.  Its 
stored  energy  was  transformed  into  external, 
mechanical  work,  i.  e„  the  moving  of  the  foot. 
Not  all  of  the  energy  set  free  takes  this  easily 
visible  form.  It  will  be  shown  later  that  much 
of  it  is  made  active  as  molecular  motion,  in  the 
form  of  heat,  chemical  action,  and  electricity. 
Agents  which  occasion  a  transformation  of 
energy  within  the  living  body  are  termed  stim- 
uli, and  tissues  which  convert  energy  of  one 
form  into  energy  of  another  in  consequence  of 
stimulation  are  said  to  be  irritable.  All  living 
tissues  are  alike  irritable,  but  the  form  in  which 
their  kinetic  or  active  energy  appears  differs 
with  the  nature  of  the  tissue.  The  contrast 
between  muscle  and  nerve  in  this  respect  is 
especially  instructive. 

Pinch  the  end  of  the  nerve. 

No  change  will  be  seen  in  the  nerve,  but  the 
muscle  will  contract. 

Thus,  while  the  most  conspicuous  form  which 
the  energy  of  muscle  takes,  when  set  free,  is 
mechanical,  the  active  nerve  does  not  alter  its 
form,  but  spends  its  energy  in  a  molecular 
change,  the  nerve  impulse,  which  passes  from 
point  to  point  along  the  nerve  to  the  muscle, 
or  gland,  or  other  structure  connected  function- 


10      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

ally  to  the  nerve.  The  effect  produced  by 
the  nerve  impulse  depends  on  the  nature  of 
the  tissue  in  which  the  nerve  ends ;  for  ex- 
ample, the  energy  set  free  in  secreting  glands 
is  especially  chemical;  that  set  free  in  the 
electrical  organ  of  Torpedo  is  especially  elec- 
trical. In  considering  these  illustrations  of  the 
ways  in  which  the  energy  of  living  tissue  may 
be  set  free,  however,  two  facts  should  always 
be  kept  in  mind ;  first,  that  by  far  the  greater 
part  of  the  stored  energy  of  the  body  is  set 
free  as  heat;  and  secondly,  that  while  the  sev- 
eral tissues  are  characterized  by  the  especial 
prominence  of  some  one  form  of  energy,  as 
contractility  in  the  case  of  muscle,  and  the 
production  and  conveyance  of  a  nerve  impulse 
in  the  case  of  nerve,  yet  the  transformation  of 
energy  in  each  tissue  is  a  complex  process, 
many  steps  of  which,  for  example  heat  and 
chemical  action,  are  common  to  all  living 
substance. 

We  have  made,  then,  the  fundamental  obser- 
vation that  an  adequate  stimulus  will  occasion 
in  muscle  a  conversion  of  latent  energy  into 
mechanical  change  in  form  and  in  the  nerve  a 
molecular  change  that  passes  along  the  nerve  as 
a  nerve  impulse.  We  must  now  examine  sys- 
tematically  the  usual    methods   of  exciting  the 


INTRODUCTION  11 

transformation  of  energy  and  inquire  concerning 
their  effect  on  muscle  and  nerve. 

Apparatus 

Normal  saline.  Bowl.  Cloth.  Pithing  wire.  Scissors. 
Forceps.  Pipette.  Glass  plate.  Cement.  Foil.  Nerve- 
holder  (filter  paper).     Muscle  clamp.     Stand.     Frog. 


12      GENERAL   PROPERTIES    OF   LIVING   TISSUES 


II 
METHODS   OF   ELECTRICAL   STIMULATION 

Introduction 

The  stimulus  most  usually  employed  in  the 
laboratory  is  electricity,  because  electricity  will 
stimulate  when  used  in  quantities  which  do  not 
destroy  the  tissues,  as  do  many  mechanical, 
chemical,  and  thermal  stimuli,  and  because  the 
intensity  and  duration  of  the  electrical  stimulus 
can  be  graduated  with  accuracy.  It  will  be 
necessary,  therefore,  to  examine  with  especial 
care  the  methods  and  the  results  of  electrical 
stimulation.  These  matters  are  involved  with 
problems  of  ionisation,  surface  tension,  osmosis, 
and  other  molecular  actions  highly  important 
in  many  fields  of  physiology.  Such  interde- 
pendent phenomena  cannot  be  studied  profitably 
without  working  hypotheses  that  shall  attempt 
to  relate  them  as  forms  of  energy. 

Kinetic  Theory.  —  The  particles  of  a  gas,  the 
simplest  state  in  which  matter  exists,  are  identi- 
cal with  its  chemical  molecules.     These  particles 


METHODS    OF    ELECTRICAL   STIMULATION         13 

are  assumed  by  Clausius  and  Maxwell  to  be  in 
constant  rapid  motion  in  all  directions.  It  is 
this  motion  which  causes  the  "disappearance" 
of  a  gas  "  set  free  "  in  the  open  air.  The  mole- 
cules of  air  are  also  in  rapid  motion  and  fre- 
quently collide  with  each  other  and  with  those 
of  the  escaping  gas,  but  the  air  molecules  are 
far  from  rilling  the  space  in  which  they  move 
and  the  molecules  of  gas  rapidly  pass  off  be- 
tween them.  In  their  flight,  they  strike  with 
a  measurable  force  whatever  opposes  them,  be 
it  another  flying  molecule  or  some  boundary 
wall.  The  force  of  the  blow  is  the  "pressure" 
of  the  molecule.  If  the  gas  be  confined  by  an 
impermeable  wall,  that  is,  a  wall  the  inevitable 
openings  in  which  are  too  small  for  the  gas 
molecules  to  pass,  the  sum  of  the  blows  of  the 
molecules  dashing  against  this  wall  will  be  the 
total  pressure  of  the  gas. 

Partial  pressure.  —  If  the  molecules  of  a  second 
gas  be  within  the  containing  vessel,  they  also 
will  strike  the  boundary.  The  force  of  their 
blows  will  be  entirely  independent  of  the  force 
of  the  blows  struck  by  the  molecules  of  the 
first  gas.  It  is  as  if  black  and  white  balls  were 
thrown  at  the  same  time  against  a  wall ;  their 
blows  would  be  independent  of  each  other. 

The  molecules  of  gas  and  the  confining  walls 


14      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

are  assumed  to  be  perfectly  elastic,  so  that  the 
motion  of  a  molecule  is  not  lost  when  it  collides 
with  another  molecule  or  strikes  the  wall;  the 
direction  of  the  flight  is  changed  but  the  swift- 
ness is  unimpaired.  The  speed  of  the  molecules 
of  a  gas  is  inversely  proportional  to  the  square 
root  of  its  density.  At  0°  C.  the  molecule  of 
oxygen  moves  at  the  rate  of  almost  eighteen 
miles  per  minute. 

Diffusion  of  gases.  —  The  molecules  of  two 
gases  moving  in  the  same  space  will  intermix 
or  "  diffuse,"  but  the  rate  will  be  surprisingly 
slow,  for  at  ordinary  pressures  the  molecules  of 
gases  are  so  near  together  that  they  cannot  move 
far  without  colliding  and  rebounding.  Their  prog- 
ress in  any  one  direction  is  thus  greatly  hindered. 

Every  particle  of  matter  attracts  every  other 
particle.  Van  der  Waal  assumes  that  with  gases 
this  attraction  is  proportional  to  the  square  of 
the  density  of  the  gas.  Where  the  density  is 
slight,  that  is,  where  there  are  few  molecules  in 
proportion  to  the  space  in  which  they  move,  this 
attraction  need  not  be  taken  into  account,  but 
where  the  confining  space  is  small,  thus  crowd- 
ing the  molecules  together,  this  attraction  be- 
comes important.  It  is  still  more  important  in 
the  case  of  liquids,  for  in  liquids  the  molecules 
are  much  nearer  than  in  a  gas. 


METHODS   OF   ELECTRICAL    STIMULATION         15 

Vapor  pressure.  —  Were  it  not  for  the  attrac- 
tive or  cohesive  force  just  mentioned,  the  mole- 
cules of  a  liquid  would  rapidly  pass  into  the 
space  surrounding  the  liquid  and  the  liquid 
would  soon  disappear  (evaporation).  But  the 
molecules  are  so  close  together  that  their  attrac- 
tion for  each  other  largely  prevents  escape. 
Nevertheless,  the  motion  of  many  of  the  mole- 
cules at  or  near  the  surface  of  the  liquid  is 
sufficient  to  break  through  this  force  of  cohesion. 
These  molecules  escape  and  their  places  are 
taken  by  molecules  which  may  in  turn  escape. 
Thus  evaporation  proceeds.  In  the  vapor  above 
the  liquid  the  escaping  molecules  collide  with 
other  molecules  and  may  be  driven  by  the  recoil 
back  into  the  liquid.  If  the  liquid  be  in  a 
confined  space,  the  number  of  vapor  molecules 
recoiling  into  the  liquid  will  increase,  partly 
because  they  are  brought  nearer  together  and 
collisions  are  thus  more  frequent  and  partly 
because  the  molecules  rebound  from  the  con- 
taining wall.  When  the  number  of  molecules 
returning  equals  the  number  leaving  the  liquid, 
the  vapor  and  the  liquid  are  in  equilibrium 
(saturation).  In  other  words,  the  vapor  tension 
or  pressure  or  force  with  which  the  liquid  mole- 
cules tend  to  leave  the  liquid  is  balanced  by  the 
gas  pressure  or  force  with  which  the  gas  mole- 


16       GENERAL    PROPERTIES    OF   LIVING   TISSUES 

cules  strike  against  the  liquid.  As  the  speed 
of  the  molecules  and  therefore  their  power  to 
escape  from  the  liquid  rises  with  the  tempera- 
ture, the  vapc?  pressure  will  also  rise  with  the 
temperature. 

Solution  of  a  gas  in  a  liquid.  —  A  liquid 
brought  near  a  gas  is  struck  by  many  of  the 
moving  molecules  of  the  gas.  Some  of  these  are 
held  by  the  attractive  force  of  the  liquid.  Some 
will  at  length  escape.  Finally,  as  the  number 
of  molecules  striking  the  surface  of  the  liquid 
remains  constant  at  the  same  pressure,  the  gas 
molecules  leaving  the  liquid  will  equal  the  number 
entering  (saturation). 

Solution  of  a  solid  in  a  liquid.  —  When  a  crys- 
talline solid  is  placed  in  a  liquid  solvent,  particles 
escape  from  the  solid  and  enter  the  liquid.  Some 
of  these  particles  again  enter  the  solid  and  are 
bound  by  it.  Saturation  is  reached  when  the 
number  of  particles  entering  and  leaving  the 
solid  is  equal. 

Solution  tension.  —  The  force  with  which  the 
particles  of  the  solid  pass  into  the  solvent  is 
termed  the  solution  tension.  There  is  equili- 
brium, i.  e.  saturation,  when  the  solution  tension 
is  balanced  by  the  force  with  which  the  particles 
in  the  solvent  return  to  the  solid. 

Osmotic    Pressure.  ■ —  It   has  been   found   that 


METHODS    OF    ELECTRICAL    STIMULATION         17 

hydrogen  gas  will  pass  through  the  metal  palla- 
dium when  the  metal  is  heated  to  200°  C.  Nitro- 
gen will  not  pass  through.  Palladium  at  200°  C. 
is  therefore  said  to  be  semi-permeable,  i.  e.  it  is  per- 
meable to  one  gas,  but  not  to  another.  If  a  tube 
of  palladium  at  200°  containing  nitrogen  gas  at 
a  pressure  of  one  half  atmosphere  be  placed  in  a 
vessel  containing  hydrogen  gas  at  a  pressure  of 
one  atmosphere,  the  hydrogen  will  pass  through 
the  palladium  into  the  tube  until  the  pressure 
of  the  hydrogen  inside  equals  that  outside  the 
tube,  namely,  oue  atmosphere.  The  pressure  in 
the  tube  will  now  be  almost  one  and  one  half 
atmospheres,  which  is  the  sum  of  the  partial 
pressure  of  the  nitrogen  (one  half  atmosphere) 
and  the  partial  pressure  of  the  hydrogen  (one 
atmosphere),  less  an  error  due  chiefly  to  the  im- 
perfect permeability  of  the  palladium.  Thus  the 
pressure  on  one  side  of  the  palladium  will  be 
higher  than  that  on  the  other  side,  as  may  be 
shown  by  connecting  the  tube  with  a  manometer. 

Substances  in  solution  may  exert  a  force  like 
the  partial  pressure  of  a  gas.  This  force  is  called 
osmotic  pressure. 

Osmotic  pressure  is  measured  most  readily  by 
the  aid  of  semi-permeable  membranes,  first  used 
for  this  purpose  by  Pfeffer.  For  demonstration 
they  may  be  made  as  follows.     Wash  a  porcelain 


18       GENEKAL   PROPEKTIES    OF   LIVING   TISSUES 

diffusion  bulb  twenty-four  hours  in  running 
water.  Dry  the  bulb  and  coat  its  neck  inside 
and  out  with  paraffin ;  when  this  has  become 
firm,  fill  the  bulb  to  above  the  lower  edge  of  the 
paraffin  with  solution  of  copper  sulphate  (2.5  gm. 
per  litre).  Place  the  bulb  in  a  beaker  and  pour 
in  a  solution  of  potassium  ferrocyanide  (2.1  gm. 
per  litre)  until  the  lower  edge  of  the  paraffin  is 
covered.  Keep  the  bulb  in  this  solution  over 
night.  Where  the  two  solutions  meet  within  the 
clay  wall  a  precipitation  membrane  of  copper 
ferrocyanide  will  form.  This  membrane  is  sup- 
ported by  the  clay  wall.  Pour  out  the  contents 
of  the  bulb  and  rinse  with  cold  distilled  water. 
Through  such  precipitation  membranes  water 
and  some  other  solvents  will  readily  pass,  while 
many  salts  dissolved  in  the  solvent  are  kept 
back. 

Fill  the  bulb  with  one  per  cent  solution  of 
cane  sugar.  Insert  in  the  neck  of  the  bulb  a 
tightly  fitting  rubber  stopper  pierced  by  a  small- 
bore glass  tube  about  ten  feet  long.  Stand  the 
bulb  in  distilled  water  and  support  the  long 
tube  in  suitable  clamps.  The  sugar  will  not  pass 
out  through  the  membrane,  but  water  will  pass 
through  it  into  the  bulb,  and  the  solution  will 
rise  in  the  tube  at  the  rate  of  several  inches  an 
hour.     The  rate  is   slow  because  the  friction  in 


METHODS    OF    ELECTRICAL    STIMULATION        19 

the  artificial  membrane  is  great ;  the  osmosis  of 
salts  through  living  membranes  may  be  very  rapid. 
When  the  liquid  in  the  tube  is  high  enough  to 
balance  the  force  with  which  the  water  would 
pass  through  the  membrane,  the  flow  ceases. 
The  difference  in  water  level  is  the  osmotic 
pressure,  the  analogue  of  gas  pressure.  The  maxi- 
mum osmotic  pressure  is  so  great  that  only  perfect 
semi-permeable  membranes  will  support  it. 

It  will  be  obvious  upon  reflection  that  osmotic 
pressure  must  be  independent  of  the  semi-per- 
meable membrane.  The  solvent  is  continuous 
through  the  membrane.  The  only  function  of 
the  membrane  is  to  render  the  osmotic  pressure 
visible. 

With  constant  temperature  the  osmotic  pres- 
sure is  nearly  proportional  to  the  concentration 
of  the  solution. 


Concentration 

Osmotic  pressure 

of  solution  of 

in  centimetres 

Ratio. 

cane-sugar. 

of  mercury. 

Per  cent. 

1 

53.5 

53.5 

2 

101.6 

50.8 

2.74 

151.8 

55.4 

4 

208.2 

52.1 

6 

307.5 

51.3 

The  osmotic  pressure  increases  as  the  tempera- 
ture rises. 


20      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

Ten  years  after  these  observations  were  pub- 
lished by  Pfeffer,  Van't  Hoff  pointed  out  the 
analogy  between  osmotic  pressure  and  gas  pres- 
sure. It  has  just  been  shown  that,  if  the  tem- 
perature be  constant,  the  osmotic  pressure  is 
proportional  to  the  amount  of  dissolved  substance 
in  a  given  volume  ;  thus  the  osmotic  pressure 
of  a  solution,  like  that  of  a  gas,  varies  inversely 
with  the  pressure.  Moreover,  the  osmotic  pres- 
sure, like  gas  pressure,  increases  with  the  tempera- 
ture. Pfeffer  observed  that  the  osmotic  pressure 
of  a  cane  sugar  solution  at  14.2°  C.  was  51  cm. 
Hg.  Assuming  that  the  osmotic  pressure,  like 
gas  pressure,  is  proportional  to  the  absolute 
temperature,  Pfeffer  then  determined  by  calcula- 
tion that  the  osmotic  pressure  of  this  same 
solution  at  32.0°  C.  should  be  54.2  cm.  Actual 
observation  gave  54.4  cm. 

In  short,  the  osmotic  pressure  of  a  dissolved 
substance  is  numerically  equal  to  the  pressure 
which  the  substance  would  exert  were  it  present 
as  a  gas. 

Plasmoiysis.  Isotony.  —  The  cells  of  Trades- 
cantia  discolor  possess  a  strong  outer  envelope 
permeable  by  both  water  and  salts,  and  a  thin 
inner  envelope  permeable  by  water,  but  not  by 
salts.  The  cell  is  filled  with  an  aqueous  solution 
of  glucose,  salts  of  malic  acid,  etc.     The  osmotic 


METHODS  OF  ELECTRICAL  STIMULATION   21 

pressure  of  the  contents  is  from  four  to  six 
atmospheres.  When  the  cell  is  placed  in  water, 
the  water  penetrates  both  envelopes  and  the  cell 
swells  so  far  as  the  resistant  outer  envelope 
may  permit.  In  a  concentrated  salt  solution, 
the  osmotic  pressure  pushes  the  inner  envelope 
away  from  the  outer  envelope,  contracting  the 
volume  of  the  cell  contents  (plasmolysis),  and 
water  leaves  the  cell  until  the  concentration  of 
the  cell  contents  equals  that  of  the  surrounding 
solution.  Solutions  whose  concentration  is  such 
that  cells  immersed  in  them  are  not  deformed 
must  possess  the  same  osmotic  pressure.  Such 
solutions  are  termed  isotonic  or  isosmotic. 

Estimation  of  Osmotic  Pressure  in  the  Blood 
Serum.  1.  The  method  of  de  Vries.1 — Make  a 
section  along  the  midrib  of  the  violet  side  of 
the  leaf  of  Tradescantia  discolor  and  two  other 
sections  one  on  each  side,  parallel  to  and  about 
2  mm.  from  the  first.  Now  make  transverse 
sections  across  the  three  vertical  sections  about 
5  mm.  apart,  and  a  final  very  thin  section  paral- 
lel to  the  surface.  Place  some  of  these  thin  tan- 
gential sections  in  the  serum  diluted  with  20  per 
cent  of  water,  and  others  in  salt  solutions  of 
different  concentrations  (0.60,  0.65,  0.70,  0.75,  0.80 

1  de  Vries:  Zeitschrift  fur  physikalische  Chemie,  1888,  ii, 
p.  419. 


22      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

per  cent).  From  time  to  time  remove  the  sec- 
tions and  observe  under  the  microscope  whether 
plasmolysis  is  present.  The  serous  fluid  that 
causes  plasmolysis  in  half  the  cells  immersed 
in  it,  is  isotonic  or  "  normal "  with  the  salt  solu- 
tion having  the  same  effect. 

For  example,  if  there  were  used  5  c.c.  serum 
+  1  c.c.  water  with  0.8  per  cent  solution  of  sodium 
chloride,  the   original   serum  would  be   isotonic 

with  a  sodium  chloride  solution  of  — — —  x  0.8 

5 

=  0.96  per  cent. 

Should  the  osmotic  pressure  of  the  serum  be 
too  slight  to  call  forth  plasmolysis  in  the  cells 
employed,  add  to  the  serum  measured  quantities 
of  a  strong  saline  solution,  e.  g.  5  per  cent  sodium 
chloride  solution.1 

2.  The  blood- corpuscle  method  of  Hamburger? 
—  Place  5  c.c.  serum  in  each  of  six  test-tubes. 
To  these  add  from  a  burette  3.1,  3.0,  2.9,  2.8,  2.7, 
and  2.6  c.c.  water,  respectively.  Into  each  tube 
let  fall  three  drops  of  defibrinated  blood,  and  mix 

1  Hamburger  :  Osmotischer  Drack  und  Ionenlehre,  1902, 
i,  p.  438. 

The  cells  of  Tradescantia  cannot  be  used  for  the  measure- 
ment of  osmotic  pressure  in  acid  solutions.  For  the  urine,  the 
cells  of  Begonia  manicata  should  be  used. 

2  HAMBURGER  :  Loc.  tit.  pp.  185  and  439.  Also  Archiv  fur 
Physiologic,  1887,  p.  31. 


METHODS   OF   ELECTRICAL   STIMULATION        23 

by  shaking,  taking  care  that  the  mixture  does 
not  foam  too  much. 

In  each  of  six  other  test-tubes  place  8  c.c. 
sodium  chloride  solution  of  0.62,  0.61,  0.60,  0.59, 
0.58,  and  0.57  per  cent,  respectively.  Into  each 
tube  let  fall  three  drops  of  the  same  defibrinated 
blood.  Mix  as  before.  After  some  hours  the 
red  corpuscles  will  have  settled  to  the  bottom 
in  all  the  tubes. 

In  the  first  series  the  clear  fluid  will  be  red 
in  some  of  the  tubes.  For  example,  the  fluid  in 
the  tubes  diluted  with  3.1,  3.0,  and  2.9  c.c.  water 
may  be  red,  while  in  the  three  other  tubes  it  may 
not  be  red.  In  this  case  the  mixture  of  5  c.c. 
serum  +  2.9  c.c.  water  has  caused  the  haemo- 
globin to  escape  from  the  corpuscles  ("  laked " 
the  blood),  while  the  mixture  of  5  c.c.  serum 
+  2.8  c.c.  water  has  not  accomplished  this. 

If  the  tubes  with  salt  solution  be  now  exam- 
ined, escaped  haemoglobin  will  be  found  only  in 
the  0.58  per  cent  and  the  weaker  solutions.     Con- 

sequently  the  mixture  of  5  c.c.  serum  H — : — ^ — — 

water  is  isotonic  with  a  sodium  chloride  solution 

.  0.59  +  0.85       _  ^0_  _ 

of  « =  0.5 8 o  per  cent.  Hence  the  un- 
diluted serum  is  isotonic  with  a  sodium  chloride 

5  _l_  2  85 
solution   of   =^ —  x  0.585  =  0.92    per    cent. 


24      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

In  a  solution  of  this  concentration  the  red  blood- 
corpuscles  of  mammals  are  in  osmotic  equi- 
librium.1    The    isotonic  (isosmotic    or    normal) 

1  In  this  calculation  it  is  assumed  that  the  osmotic  pressure 
is  proportional  to  the  concentration.  This  is  not  strictly  cor- 
rect. When  serum  is  diluted  with  an  equal  volume  of  water, 
the  osmotic  pressure  of  the  resulting  liquid  is  not  merely  half 
so  large  as  before,  but  is  somewhat  greater  than  one  half  the 
original  pressure.  For  when  the  water  is  added,  a  part  of  the 
molecules  not  yet  dissociated  are  split  into  ions  and  each  ion 
has  an  osmotic  pressure  equal  to  that  of  an  undissociated  mole- 
cule. If  the  serum  upon  dilution  with  water  followed  the 
same  dissociation  curve  as  the  sodium  chloride  solution  of  0.92 
per  cent,  the  above  method  of  calculation  would  be  strictly 
correct.  This  is,  however,  not  the  case  ;  on  the  contrary,  the 
dissociation  curves  separate  from  each  other.  But  this  devia- 
tion, in  the  case  of  the  dilutions  considered  here,  lies  within 
the  limit  of  errors  of  observation,  probably  because  the  osmotic 
pressure  of  the  serum  is  due  chiefly  to  sodium  chloride  (Ham- 
burger, p.  186). 

The  above  calculation  also  leaves  out  of  account  the  fact 
that  the  blood-corpuscles  are  permeable  for  anions.  It  is  evi- 
dent that  the  exchange  of  ions  between  blood-corpuscles  and 
surrounding  liquid  will  differ  according  as  this  liquid  is  dilute 
serum  or  pure  sodium  chloride  solution.  For  the  partial  ten- 
sion of  the  ions  in  the  two  solutions  is  not  the  same.  The 
partial  pressure  of  the  CI'  ions  in  the  0.6  per  cent  sodium 
chloride  solution  is  greater  than  in  the  serum  diluted  with  60 
per  cent  water;  while  in  the  serum  there  is  a  pressure  of 
CO'"  ions,  lacking  in  the  sodium  chloride  solution.  Moreover, 
the  blood-corpuscles  placed  in  these  liquids  acquire  a  different 
composition.  The  osmotic  pressure  of  the  blood-corpuscles  is 
increased  by  immersion  in  sodium  chloride  solution. 

Dissociation  and  permeability  act  with  opposite  sign,  balanc- 
ing each  other.     That  the  blood-corpuscle  method  is  practically 


METHODS   OF   ELECTRICAL   STIMULATION 


25 


concentration  for  the  corpuscles  of  frog's  blood  is 
0.6  per  cent. 

Surface  Tension.  —  The  osmotic  pressure  of 
solutions  is  very  great.  In  the  ordinary  reagents 
of  the  laboratory  it  amounts  to  many  atmos- 
pheres. Obviously,  such  solutions  could  not  be 
kept  in  thin  glass  beakers  or 
bottles  were  these  enormous 
pressures  not  restrained  by 
some  opposing  force.  This  op- 
posing force  is  surface  tension, 
which  acts  with  a  pressure  of 
probably  hundreds  of  atmos- 
pheres upon  the  free  surface  of 
a  liquid,  whether  that  surface 
be  bounded  by  air  or  glass. 
The  semi-permeable  membrane 
is  filled  with  liquid,  and  there- 
fore does  not  present  a  free 
surface. 

1.  A  thick  wire  is  bent  to  enclose  a  right- 
angled  space  and  the  end  prolonged  for  a  handle. 
(Fig.  1.)  A  very  fine  slack-wire  divides  the  space 
in  halves. 


Fig.  4.     The  tension 
indicator. 


accurate  may  be  shown  by  comparison  with  the  method  of 
estimating  osmotic  pressure  by  the  depression  in  the  freezing- 
point  of  the  solution,  which  is  proportional  to  the  concentration 
of  the  solution  (p.  439). 


26      GENERAL   PROPERTIES   OF   LIVING-   TISSUES 

Dip  the  tension  indicator  into  a  soap  solution. 

A  thin  layer  of  the  solution  will  span  the 
frame  on  both  sides  of  the  dividing  wire.  The 
tension  of  the  membrane  on  one  side  of  the  di- 
viding wire  compensates  that  on  the  other  and 
the  wire  will  not  move. 

Hold  the  frame  in  a  vertical  position.  The 
cross  wire  will  sink  slightly,  owing  to  the  force 
of  gravity.  Absorb  the  lower  membrane  with 
filter  paper. 

The  cross  wire  will  at  once  be  lifted  against 
the  force  of  gravity  by  the  surface  tension  of  the 
remaining  membrane.  Destroy  the  remaining 
membrane  and  the  wire  will  fall  again. 

2.  Strew  lycopodium1  upon  a  water  surface. 
In  the  centre  place  a  few  drops  of  alcohol. 

The  lycopodium  will  be  driven  in  all  direc- 
tions. The  surface  tension  of  alcohol  is  less 
than  that  of  water.  The  water-air  surface  and 
the  alcohol-air  surface  are  therefore  not  in 
equilibrium.  The  water-air  surface  contracts 
violently,  and  the  alcohol-air  surface  expands, 
producing  the  strong  currents  made  visible  by 
the  motion  of  the  lycopodium. 

Electrolysis.  —  1.  Connect  two  dry  cells  in 
series  (carbon  of  one  cell  connected  with  zinc  of 
other).     Attach  wires  to  the  terminal  zinc  and 

1  Be  careful  not  to  bring  the  tycopotliuni  near  a  flame. 


METHODS    OF   ELECTRICAL   STIMULATION        27 

carbon.  Touch  the  ends  of  the  wires  together. 
An  electric  current  passes,  as  evidenced  by  the 
spark  when  the  contact  is  made  or  broken,  but 
no  material  change  can  be  observed  in  the  me- 
tallic conductor. 

2.  Place  two  pieces  of  platinum  foil  in  a  solu- 
tion of  copper  sulphate  and  connect  them  to  the 
terminal  zinc  and  carbon  as  before.  Copper  will 
be  deposited  on  the  platinum  connected  with  the 
zinc,  and  oxygen  will  be  deposited  on  the  plati- 
num connected  with  the  carbon.  Thus  the 
passage  of  the  current  through  the  conducting 
solution  or  electrolyte  has  caused  a  change  in 
the  solution,  evidenced  by  a  movement  of  pon- 
derable matter. 

Faraday  discovered  that  the  quantity  of  matter 
moved  by  the .  current  was  always  proportional 
to  the  quantity  of  the  current,  independent  of 
its  strength  or  speed.  In  the  electrolysis  of 
hydrochloric  acid  96,500  coulombs  1  will  set  free 
1  gm.  of  hydrogen.  Faraday  also  discovered 
that  the  same  quantity  of  current  (96,500  cou- 
lombs) which  carries  1  gm.  of  hydrogen  will 
carry  the  chemical  equivalent  of  any  other  sub- 

1  A  coulomb  (ampere)  of  electricity  is  the  quantity  of  cur- 
rent which,  when  passed  through  a  solution  of  silver  nitrate  in 
water,  deposits  silver  on  the  cathode,  or  negative  pole,  at  the 
rate  of  0.001118  gram  per  second. 


28      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

stance,  for  example  35.5  gm.  of  chlorine.  In  the 
above  experiment  on  the  electrolysis  of  copper 
sulphate  solution,  each  31.5  grams  of  copper 
moved  to  the  zinc  pole  requires  the  passage  of 
exactly  96,500  coulombs.  The  particles  of  matter 
travelling  in  the  solution  toward  the  anode  were 
called  by  Faraday  the  anions  and  those  travel- 
ling toward  the  cathode  were  called  cations.  On 
reaching  the  poles  the  ions  give  up  their  electric 
charge  and  resume  their  simple  chemical  nature. 
Thus  each  31.5  grams  of  copper  ions,  on  reaching 
the  cathode,  gives  up  96,500  coulombs  of  electric- 
ity and  becomes  ordinary  copper  again,  and  each 
96  grams  of  sulphate  ions  gives  up  96,500  cou- 
lombs and  becomes  the  ordinary  radical  S04. 
This  radical  cannot  exist  uncombined  in  water, 
but  forms  sulphuric  acid.  S04  +  H20  =  H2S04 
+  O.  Thus  the  liquid  around  the  anode  becomes 
acid,  and  actual  measurement  has  shown  that  the 
quantity  of  sulphuric  acid  formed  at  the  anode 
is  exactly  equivalent  to  the  quantity  of  copper 
deposited  on  the  cathode. 

The  ions  move  very  slowly.  The  high  vis- 
cosity or  internal  friction  of  the  liquid  opposes  a 
great  resistance  to  the  movement  of  ions  as  well 
as  to  the  osmosis  of  dissolved  substances.  To 
drive  1  gm.  of  hydrion  (OH)  through  pure  water 
at  the  rate  of  1  cm.  per  second,  a  force  equal  to 


METHODS    OF    ELECTRICAL    STIMULATION         29 

320,000  tons'  weight  is  required.  To  diffuse 
1  gm.  urea  through  pure  water  at  the  rate  of 
1  cm.  per  second,  40,000  tons'  weight  is  required. 
In  dilute  aqueous  solutions  at  18°  C.  a  difference 
of  potential  of  1  volt  between  electrodes  1  cm. 
apart  will  drive  the  cation  H  10.8  cm.  per  hour, 
the  cation  Na  1.26  cm.,  the  anion  OH  5.6  cm., 
and  the  anion  CI  2.12  cm.  per  hour. 

As  the  ions  move  so  slowly  and  as  the  products 
of  electrolysis  appear  at  each  electrode  the 
moment  the  current  is  made,  it  is  evident  that 
the  ions  which  immediately  appear  at  the  anode 
cannot  be  derived  from  the  same  molecules  as  the 
ions  which  simultaneously  appear  at  the  cathode. 

"  Clausius  explains  this  in  the  following  way : 
According  to  the  theory  of  molecular  motion,  of 
which  he  has  himself  been  the  chief  founder, 
every  molecule  of  the  fluid  is  moving  in  an  ex- 
ceedingly irregular  manner,  being  driven  first  one 
way  and  then  another  by  the  impacts  of  other 
molecules  which  are  also  in  a  state  of  agitation. 

"  This  molecular  agitation  goes  on  at  all  times 
independently  of  the  action  of  electromotive  force. 
The  diffusion  of  one  fluid  through  another  is 
brought  about  by  this  molecular  agitation,  which 
increases  in  velocity  as  the  temperature  rises.  The 
agitation  being  exceedingly  irregular,  the  encoun- 
ters  of   the    molecules  take  place  with  various 


30      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

degrees  of  violence,  and  it  is  probable  that  even  at 
low  temperatures  some  of  the  encounters  are  so 
violent  that  one  or  both  of  the  compound  molecules 
are  split  up  into  their  constituents.  Each  of  these 
constituent  molecules  now  knocks  about  among 
the  rest  till  it  meets  with  another  molecule  of 
the  opposite  kind,  and  unites  with  it  to  form  a 
new  molecule  of  the  compound.  In  every  com- 
pound, therefore,  a  certain  proportion  of  the 
molecules  at  any  instant  are  broken  up  into  their 
constituent  atoms. 

"  Now  Clausius  supposes  that  it  is  on  the  con- 
stituent molecules  in  their  intervals  of  freedom 
that  the  electromotive  force  acts,  deflecting  them 
slightly  from  the  paths  they  would  otherwise 
have  followed,  and  causing  the  positive  constit- 
uents to  travel,  on  the  whole,  more  in  the  positive 
than  in  the  negative  direction,  and  the  negative 
constituents  more  in  the  negative  direction  than 
in  the  positive.  The  electromotive  force,  there- 
fore, does  not  produce  the  disruptions  and  reunions 
of  the  molecules,  but,  finding  these  disruptions 
and  reunions  already  going  on,  it  influences  the 
motion  of  the  constituents  during  their  intervals 
of  freedom."  1 

1  Quoted  from  Clerk  Maxwell  by  Walker  in  his  admirable 
"Introduction  to  Physical  Chemistry,"  a  book  to  which  the 
present  writer  is  much  indebted. 


METHODS    OF    ELECTRICAL    STIMULATION        31 

Views  of  Arrhenius.  —  It  was  Arrhenius  who 
made  these  ideas  regarding  the  dissociation  of 
the  molecules  of  solutions  into  ions  quantitative 
and  thus  precise.  Feeble  electrolytes,  i.  e.  poor 
conductors  of  electricity,  are  but  slightly  dis- 
sociated, whereas  solutions  that  readily  conduct 
electricity  are  largely  dissociated.  Ionisation 
may  be  measured  by  the  degree  of  conductivity. 
Undissociated  molecules  carry  no  electricity.  Each 
univalent  ion  has  the  same  load :  96,500  coulombs. 

Conductivity  depends  on  the  number  of  the 
ions  and  upon  their  speed.  In  this  connection 
the  following  observation  is  of  interest.  If  suc- 
cessive quantities  of  pure  water  be  added  to  a 
salt  solution,  the  conductivity  will  increase  as 
the  dilution  increases.  The  first  factor  to  be 
considered  here  is  the  viscosity  of  the  solution, 
for  the  viscosity  determines  the  resistance  of  the 
solution  to  the  passage  of  ions,  and  thus  determines 
the  speed  of  the  ions.  As  the  addition  of  water 
continues  a  point  is  soon  reached  at  which  the 
amount  of  water  in  the  solution  is  so  great  in 
relation  to  the  amount  of  salt  that  the  water  may 
be  regarded  practically  as  pure.  The  addition 
of  more  water  should  not  then  appreciably  affect 
the  viscosity  and  thus  the  speed  of  the  ions.  If 
the  conductivity  were  related  solely  to  the  speed 
of   the  ions,  the   conductivity   should  not  then 


32      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

increase  upon  this  further  addition  of  water. 
Observation  shows  that  it  does  increase.  It 
must  therefore  depend  on  the  degree  of  dissocia- 
tion, i.  e.  the  number  of  ions. 

When  the  solution  is  heated,  its  viscosity  and 
thus  its  fluid  friction  diminishes ;  the  ions  pass 
through  it  with  less  difficulty  and  the  conduc- 
tivity rises.  Non-conducting  substances  added 
to  aqueous  solutions  may  affect  both  the  number 
and  the  speed  of  the  ions.  The  first  additions 
of  alcohol  to  a  dilute  solution  increase  the  vis- 
cidity, and  lessen  the  speed  of  the  ions ;  after  a 
certain  limit,  further  additions  have  little  effect 
on  the  speed,  but  markedly  lessen  the  number 
of  the  ions,  i  e.  the  degree  of  ionisation  or  dis- 
sociation. Comparisons  of  electrical  conductivity 
in  solutions  of  different  concentration  can  be 
made  only  when  the  rate  at  which  the  ions 
move  remains  the  same ;  in  other  words,  the 
salt,  the  solvent,  and  the  temperature  must  be 
the  same  in  the  two  solutions. 

Electrolytic  solution  Pressure.  —  When  a  salt 
is  placed  in  water  it  dissolves  until  its  solution 
pressure  or  tendency  to  pass  into  solution  is 
balanced  by  the  osmotic  pressure  of  the  dissolved 
particles.  If  the  osmotic  pressure  exceed  the 
solution  pressure,  salt  will  be  deposited.  As 
the  salt  dissolves,  positive  and  negative  ions  are 


METHODS    OF   ELECTRICAL    STIMULATION        33 

formed  in  equivalent  quantities,  so  that  there  is 
no  difference  in  electrical  pressure. 

When  metallic  zinc  is  placed  in  dilute  sulphu- 
ric acid,  it  dissolves,  and  positively  charged  zinc 
ions  enter  the  solvent,  but  no  negative  ions  are 
formed  at  the  same  time.  The  solution  next 
the  metal  becomes  statically  charged  with  posi- 
tive electricity,  and  in  consequence  the  zinc  itself 
becomes  negatively  charged.  The  electrical  stress 
thereby  produced  compensates  the  difference 
between  the  osmotic  pressure  of  the  zinc  ion  and 
the  electrolytic  solution  pressure  of  the  zinc. 

When  copper  is  placed  in  a  solution  of  copper 
sulphate,  the  osmotic  pressure  of  the  metal  ion 
exceeds  the  electrolytic  solution  pressure  of  the 
metal  and  metallic  copper  is  deposited  on  the 
surface  of  the  electrode.  The  metal  becomes 
positively  charged  and  the  solution  negatively 
charged  through  the  sulphanions  that  gather  at 
the  layer  of  solution  next  the  metal.  This  pro- 
cess continues  until  the  electrical  stress  balances 
the  difference  between  the  actual  osmotic  pres- 
sure and  the  electrolytic  solution  pressure. 

The  electrical  double  layer  about  each  elec- 
trode is  of  only  molecular  thickness,  so  that  the 
solution  or  deposition  of  an  extremely  small 
quantity  of  metal  is  sufficient  to  establish  equi- 
librium. 


o4      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

In  galvanic  cells,  in  which  two  metals  are 
immersed  in  one  or  more  electrolytes,  there  are 
three  sources  of  electromotive  force:  the  junc- 
tion of  the  metals  with  the  electrolytes,  the 
junction  of  the  two  metallic  conductors,  and  the 
junction  of  the  electrolytes.  The  junction  of 
the  metals  with  the  electrolytes  is  the  principal 
source ;  the  electromotive  force  produced  by  the 
junction  of  the  metals  is  slight,  and  the  ions  of 
different  neutral  salts  move  at  not  far  from  the 
same  speed,  so  that  the  electromotive  force  at  the 
junction  of  the  electrolytes  is  also  relatively 
small. 

The  Electrometer,  the  Eheocord,  and 
the  Cell 

In  order  to  study  differences  in  electrical 
potential,1  a  galvanometer  or  some   other   elec- 

1  The  difference  of  potential  may  be  compared  to  the  differ- 
ence of  water  level  between  a  reservoir  and  its  distributing 
pipes.  It  produces  an  electromotive  force,  comparable  to  the 
force  which  moves  the  water  from  the  higher  to  the  lower  level. 
The  unit  of  electrical  pressure  is  the  volt.  The  flow  through 
an  hydraulic  system  is  measured  by  the  quantity  of  water  pass- 
ing any  point  in  a  given  time  ;  similarly  the  quantity  of  elec- 
tricity is  the  amount  that  flows  through  a  cross-section  of  the 
conductor  in  a  given  time.  The  unit  of  quantity  is  the  ampere. 
Electricity  passing  through  a  conductor  meets  with  a  resistance 
which  becomes  greater  as  the  cross-section  of  the  conductor 


METHODS   OF   ELECTRICAL    STIMULATION         35 

trometer  is  necessary.  In  the  galvanometer,  the 
points  of  different  potential  are  connected  by  a 
coil  of  wire  near  which  is  suspended  a  magnet. 
When  the  circuit  is  completed,  the  electrical 
energy  acts  on  the  suspended  magnet  by  induc- 
tion, and  deflects  it  to  an  extent  proportionate 
to  the  difference  of  potential.  In  the  capillary 
electrometer,  which  is  the  electrometer  preferred 
here,  a  capillary  tube  filled  with  mercury  and 
sulphuric  acid  dips  in  a  wider  tube  which  con- 
tains sulphuric  acid.  The  points  the  potential 
of  which  is  to  be  measured  are  connected  with 
the  mercury  and  the  acid  respectively.  When 
the  connection  is  made,  the  tension  of  the  sur- 
face of  mercury  in  contact  with  the  acid  changes, 
causing  the  mercury  to  move  in  the  capillary. 
The  change  in  surface  tension  is  proportional  to 

diminishes,  just  as  water  can  be  forced  more  easily  through 
wide  channels  than  through  narrow  ones.  The  unit  of  electri- 
cal resistance  is  the  ohm.  The  precise  definition  of  these  units 
is  as  follows  : 

A  volt  is  the  electromotive  force  that,  steadily  applied  to  a 
conductor  whose  resistance  is  one  international  ohm,  will  pro- 
duce a  current  of  one  international  ampere.  The  practical 
ampere  {coulomb)  is  the  unvarying  current  which,  when  passed 
through  a  solution  of  nitrate  of  silver  in  water,  deposits  silver 
on  the  cathode,  or  negative  pole,  at  the  rate  of  0.001118  gram 
per  second.  The  ohm  is  the  resistance  offered  to  an  unvarying 
electrical  current  by  a  column  of  mercury  at  the  temperature 
of  melting  ice,  14.4521  grams  in  mass,  of  a  constant  cross- 
sectional  area,  and  of  the  length  of  106.3  centimetres. 


36      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

the  difference  in  potential.  The  action  of  the 
instrument  will  be  more  clear  from  the  follow- 
ing experiments. 

Surface  Tension  altered  by  Electrical  Energy.  — 
In  a  small  porcelain  evaporating  dish  place  a 
globule  of  mercury  about  one  inch  in  diameter. 

The  cohesion  of  the  mercury  is  stronger  than 
the  attraction  between  the  mercury  and  porce- 
lain, —  the  mercury  does  not  "  wet "  the  porcelain. 
The  free  surface  of  the  mercury  is  curved  and 
not  plane,  as  it  would  be  were  the  molecules 
acted  upon  by  the  force  of  gravity  alone.  Obvi- 
ously the  spreading  of  the  mercury  is  resisted  by 
some  force  that  strives  to  make  the  drop  spher- 
ical, i.  e.  to  make  the  surface  as  small  as  possible. 

This  force  is  called  the  surface  tension.  It  is 
the  attraction  which  the  molecules  beneath  the 
surface  exert  on  the  side  of  the  surface  layer 
next  them.  The  form  of  the  drop  is  the  result 
of  the  equilibrium  between  these  opposing  forces 
(Thomas  Young,  1804). 

Cover  the  mercury  one  centimetre  deep  with 
5  per  cent  sulphuric  acid.  Note  carefully  the 
degree  of  convexity.  Add  a  trace  of  potassium 
bichromate.     The  drop  will  flatten  slightly. 

When  a  metal  is  placed  in  an  electrolyte,  a 
difference  of  potential  is  created  at  the  surfaces 
in  contact.      If  the  metal  is  positive  compared 


METHODS   OF   ELECTRICAL   STIMULATION        37 

with  the  electrolyte,  an  immeasurably  thin  layer 
of  positively  electrified  molecules  may  be  said  to 
coat  its  surface,  and  in  the  electrolyte  a  parallel 
layer  of  negatively  electrified  molecules  will 
collect.  On  every  side  of  the  parallel  layer 
electricity  of  the  same  sign  will  be  repelled.  In 
the  case  of  a  liquid  metal,  for  example  mercury, 
the  form  of  the  surface  will  be  altered,  for  the 
repulsion  of  like  electricities  will  tend  to  stretch 
the  surface  layer,  and  will  thus  oppose  the  sur- 
face tension.  The  new  form  which  the  surface 
will  take  is  the  equilibrium  between  the  electri- 
cal energy  and  the  surface  tension  (Helmholtz). 
If  this  equilibrium  is  changed  by  the  introduc- 
tion of  new  electrical  energy,  the  curvature  of 
the  surface  will  change  (Henry). 

Fasten  an  iron  wire  in  the  muscle  clamp  and 
clamp  the  latter  to  the  stand.  Bring  the  wire 
over  the  mercury  and  lower  the  muscle  clamp 
until  the  wire  just  touches  the  edge  of  the 
mercury.     Fix  the  clamp  in  this  position. 

The  instant  the  two  metals  touch  (iron  and 
mercury  in  chromic  acid  solution)  the  existing 
difference  of  potential  will  be  altered.  The  sur- 
face tension  will  thereby  be  increased  and  the 
globule  will  become  more  convex.  This  move- 
ment withdraws  the  margin  of  the  globule  from 
the  iron   and   the   globule  flattens  again,  which 


38      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

brings  it  again  into  contact  with  the  iron.  This 
play  is  repeated  until  the  chromic  acid  is  all 
reduced  to  chromic  sulphate. 


A      ,  B 

Fig.  5.    Stage  electrometer;1  about  three-sevenths  the  actual  size.    A, 
Side  view.    B,  Front  view. 

The  Electrometer. — -The  electrometer  consists  of 
a  vertical  tube  drawn  out  at  the  lower  end  into  a 
fine  capillary  and  filled  with  mercury.     (Fig.  5.)    The 

1  Science,  1905,  xxii,  p.  602. 


METHODS    OF   ELECTRICAL   STIMULATION        39 

upper  end  of  the  tube  is  joined  to  a  cylinder  in  which 
a  piston  is  moved  by  a  screw,  thus  making  pressure 
on  the  mercury  column.  The  end  of  the  capillary  dips 
in  a  reservoir  containing  twenty  per  cent  sulphuric 
acid.  Platinum  wires  lead  from  the  acid  reservoir 
and  the  mercury  in  the  capillary  to  convenient  bind- 
ing posts.  The  platinum  wire  should  never  touch 
the  acid,  but  should  be  protected  by  a  covering  of 
mercury.  When  mercury  is  placed  in  the  vertical 
tube  it  enters  the  capillary  until  the  weight  of  the 
column  of  mercury  is  balanced  by  the  surface  tension, 
which  is  inversely  proportional  to  the  diameter  of  the 
tube.  If  the  capillary  be  now  dipped  in  the  reservoir 
containing  the  sulphuric  acid,  and  the  piston  driven 
upward  by  its  screw,  mercury  will  be  forced  out  of  the 
capillary  into  the  acid ;  and  on  lowering  the  pressure 
the  mercury  will  retreat  within  the  capillary,  drawing 
the  acid  after  it.  Numerous  advantages  are  presented 
by  this  form  of  electrometer.  It  tits  the  stage  of  the 
microscope.  The  microscope  need  not  be  tilted  very 
far,  and  the  observer  is  therefore  in.  a  comfortable 
position.  The  position  of  the  electrometer  on  the 
stage  may  readily  be  changed.  All  the  parts  near  the 
acid  are  of  hard  rubber,  thus  excluding  currents  that 
might  arise  from  acid  touching  metal  parts.  The 
acid  tube  is  flanged  so  that  the  acid  cannot  creep 
out  along  the  capillary  tube.  The  capillary  can 
easily  be  brought  against  the  wall  of  the  acid  tube. 
The  tube  from  which  the  capillar}7  springs  descends 
within  the    acid   tube,   thus  protecting  the  capillary 


40      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

against  breakage.  Either  tube  may  at  once  be  re- 
moved from  its  holder.  The  platinum  wires  extend 
to  the  binding  post,  and  are  not  simply  short  pieces 
soldered  to  copper  wire.  The  wire  to  the  capillary 
tube  extends  to  the  bottom  of  the  tube,  thus  main- 
taining the  contact  until  all  the  mercury  in  the  tube 
is  used. 

About  one  cubic  centimetre  of  paraffin  oil  should 
be  placed  above  the  piston.  Only  absolutely  clean 
double-distilled  mercury  should  be  used. 

As  the  mercury  in  the  capillary  is  kept  from 
falling  by  the  surface  tension,  it  is  obvious  that 
whatever  increases  or  diminishes  the  surface 
tension,  for  example  an  electric  current,  will 
raise  or  lower  in  corresponding  measure  the 
mercury  in  the  capillary.  The  alteration  in  sur- 
face tension  is  accompanied  by  the  movement 
of  ions  between  the  meniscus  and  the  remaining 
electrode  of  the  electrometer  (the  mercury  in 
the  acid  reservoir).  In  practice  it  is  found  that 
this  movement  can  be  neither  very  rapid  nor 
long  continued,  without  injuring  the  sensitiveness 
of  the  instrument.  The  potential  difference 
from  even  a  single  element  (Daniell  or  dry  cell) 
is  far  too  large  to  be  used  safely.  It  is  advisable 
to  employ  a  potential  divider,  or  rheochord,  which 
shall  permit  only  a  fraction  of  the  original 
potential  (not  more  than  0.1  volt)  to  reach  the 


METHODS    OF   ELECTRICAL   STIMULATION         41 

electrometer.  The  platinum  should  never  come 
in  contact  with  the  acid. 

The  electrometer  should  be  kept  short-cir- 
cuited, except  during  an  observation,  so  that 
the  capillary  and  the  mercury  in  the  reservoir 
may  always  be  connected  through  a  conductor. 
The  short-circuit  key  is  shown  in  Fig.  5,  B. 
A  strip  of  spring  brass  connected  with  one 
of  the  binding  posts  of  the  electrometer  rests 
against  a  second  piece  of  brass  connected  with 
the  other  binding  post,  except  when  depressed 
by  the  finger.  The  point  of  higher  potential, 
when  known,  should  always  be  connected  with 
the  capillary. 

When  the  capillary  electrometer  is  connected 
with  two  points  of  unlike  potential  the  meniscus 
is  displaced.  The  pressure  necessary  to  bring 
it  back  to  its  original  position  is  proportional  to 
the  electromotive  force  that  displaced  the  me- 
niscus. Thus  by  connecting  the  electrometer 
with  known  differences  of  potential  it  may  be 
experimentally  graduated.  In  practice,  the  re- 
lation between  the  pressure  and  the  potential 
must  frequently  be  redetermined.  It  is  usually 
easier  to  measure  differences  of  potential,  such 
as  the  demarcation  current  of  nerve  or  muscle, 
by  compensation  (Fig.  47,  p.  294).  In  this  method 
the  electromotive  force  of  the  demarcation  current 


42      GENERAL   PROPERTIES   OF  LIVING  TISSUES 

is  measured  in  fractions  of  a  Daniell  cell,  or  any 
other  constant  element,  by  bringing  into  the  same 
circuit  with  the  current  of  injury,  but  in  an  op- 
posite direction,  so  much  of  the  current  from  the 
cell  as  will  exactly  balance  the  current  of  injury, 
i.  e.  so  much  as  will  keep  the  meniscus  of  the 
electrometer  from  moving  in  either  a  positive 
or  negative  direction  when  connected  with  the 
circuit. 

Advantages  of  the  Electrometer.  —  The  mass  of 
mercury  displaced  in  the  movement  of  the  menis- 
cus is  very  small,  and  the  distance  through  which 
it  is  moved  is  short.  Hence  the  inertia  of  posi- 
tion is  easily  overcome  and  the  inertia  of  motion 
(which  is  proportionate  to  the  mass  times  the 
square  of  the  velocity)  is  practically  wanting. 
The  absence  of  inertia  errors,  the  almost  instan- 
taneous quickness  with  which  the  meniscus  takes 
its  new  position,  the  ease  with  which  slight  elec- 
tromotive forces  (io"o7nr  vo^)  may  be  measured, 
and  simplicity  of  construction,  are  the  principal 
advantages  of  this  admirable  instrument. 

The  Rheochord.  —  If  two  poles  of  a  cell  or 
other  points  of  different  potential  be  joined  by 
a  well-drawn  wire,  the  potential  through  the 
wire  will  fall  uniformly  from  the  anode  to  the 
cathode.  The  greater  the  resistance  in  the  wire, 
the  more  uniform  will  be  the  fall  in  potential. 


METHODS   OF   ELECTRICAL    STIMULATION        43 

The  Long  Rheochord.  —  In  the  long  rheochord 
(Fig.  6)  a  metre  rule  is  screwed  upon  a  wood 
base.  At  each  end  is  a  binding  post.  To  post  0  is 
fastened  the  end  of  an  unbroken  German-silver  wire 
twenty  metres  in  length.  This  wire  is  carried  along 
the  metre  stick  to  the  second  post,  1,  then  wound 
upon  a  spool,  and  the  end  fastened  to  a  third  binding 


Fig.  6.     The  long  rheochord  ;  about  one-thirteenth  the  original  size. 

post.  The  wire  upon  the  metre  rule  is  bare,  the 
remaining  nineteen  metres  silk-covered.  A  conven- 
ient spring  contact  with  binding  post  slides  along  the 
metre  rule. 

The  Square  Rheochord.  —  Upon  a  block  of  hard 
maple,  12.5  cm.  square,  is  placed  a  centimetre  scale 
beginning  at  the  0-post  shown  on  the  left  side  of 
Fig.  7  and  ending  at  the  1 -metre  post  visible  in 
the  background  to  the  left.  For  the  sake  of  clearness 
the  numbers  on  this  scale  have  been  omitted  from  the 
figure.  Along  the  scale,  between  these  two  posts,  is 
stretched  the  first  metre  of  a  continuous  German-silver 
wire,  0.26  mm.  in  diameter  and  twenty  metres  long. 
The  remaining  nineteen  metres  of  this  wTire  are  coiled 
upon  a  spool,  and  the  free  end  is  fastened  to  the 
tw7enty-metre  post  shown  in  the  background  to  the 
right  of  Fig.  7.     One  of  the  posts  may  be  turned,  in 


44      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

order  to  keep  the  wire  taut,  in  case  changes  of  tem- 
perature have  caused  it  to  lengthen.  (This  device  is 
not  shown  in  Fig.  7.)  The  under  surface  of  the  con- 
tact block  is  bevelled  so  that  the  metal  touches  the 
wire  only  with  one  edge  ;  the  opposite  edge  is  sup- 
ported by  a  piece  of  hard  rubber. 

A  flexible  cable  leads  from  the  contact  block  to  the 
binding  post  shown  in  the  foreground  to  the  right. 


Fig.  7.     The  square  rheochord  ;  two-fifths  the  actual  size.1 

The  resistance  in  the  20  metres  of  thin  Ger- 
man-silver wire  is  so  great  (about  184  ohms) 
that  the  internal  resistance  of  the  element  fur- 
nishing the  electromotive  force,  together  with  the 
resistance  of  the  large  copper  connecting-wires, 
practically  disappears  for  such  measurements  as 
we  shall  need  to  make.  As  the  fall  of  potential 
is  uniform  throughout  the  20  metres,  the  differ- 

1  American  Journal  of  Physiol ogy,  1903,  viii,  p.  xli. 


METHODS   OF   ELECTRICAL   STIMULATION         45 

ence  of  potential  between  post  0  and  post  1  will 
be  practically  one-twentieth  the  electromotive 
force  of  the  element.  Thus  when  the  sliding 
contact  is  at  post  1,  the  capillary  electrometer 
receives  one-twentieth  the  electromotive  force  of 
the  element.  By  moving  the  slider  from  post  1 
towards  post  0,  any  desired  fraction  of  this  one- 
twentieth  may  be  measured  by  the  electrometer. 

The  Simple  Key.  —  A  copper  bar  with  hard  rubber 
handle  is  pivoted  at  one  end  in  a  brass  post  with 
binding  screw  for  electrical 


connection  (Fig.  8).     Xear      CP  /^  P 

the  other  end  of  the  bar  is 
a  platinum  ■  pin,  which, 
when  the  key  is  closed, 
rests  upon  a  platinum  plate 


borne  Upon  a    Second  bind-         Fig.  S.     The   simple  key ;   about 

three -eighths  the  actual  size.    The 
ing  post.  wire  spriug  which  presses  the  bar 

The  contact  bar  is  held    afinst  the  contact  plate  is  not 

shown. 

against   the    contact   plate 

partly  by  its  own  weight  and  partly  by  a  wire  spring 
not  shown  in  Fig,  8.  When  it  is  desired  to  break  the 
circuit  the  contact  bar  is  turned  back. 

Many  experiments  in  physiology  require  stimuli  of 
uniform  intensity.  Variations  in  the  make  or  break  of 
the  current  due  to  faults  in  the  contacts  of  the  key  in 
the  primary  circuit  are  a  frequent  source  of  error. 
With  the  key  described  here  the  break  in  the  circuit 
may  be  made  practically  uniform. 


46      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

The  Short-circuiting  Key.  —  Two  strips  of  brass, 
provided  with  a  binding  post  at  each  end,  are  fastened 
to  a  block  of  dark  slate  (Fig.  9).  At  the  centre  of 
one  strip  is  a  post  in  which  is  pivoted  a  copper  bar 
ending  in  a  hard-rubber  handle.  The  bar  may  be 
lowered  between  edges  of  spring  brass. 

Polarization.  —  Connect  a  platinum  and  a  zinc * 
plate  through  a  simple  key  with  posts  0  and  20 


Fig.  10. 


Fig.  9.    The  short-circuiting  key ; 
about  three-eighths  the  actual  size. 


of  the  rheochord  as  shown  in  Fig.  10.  Connect 
the  zero  post  and  the  slider  with  the  capillary 
electrometer  through  a  short-circuiting  key. 

1  It  will  be  observed  that  the  zinc  is  amalgamated.  Chemi- 
cally pure  zinc  does  not  need  amalgamation.  Commercial  zinc 
contains  iron,  arsenic,  etc.,  as  impurities.  The  contact  of  una- 
malgamated  zinc  and  these  dissimilar  metals  with  an  electrolyte 
creates  a  difference  of  potential,  and  parasitic  currents  run  from 
the  zinc  to  the  foreign  metals.  These  currents  are  prevented  by 
covering  the  impurities  with  zinc  amalgam,  the  electromotive 
properties  of  which,  toward  sulphuric  acid,  are  those  of  pure 
zinc.  As  the  zinc  in  the  amalgam  dissolves  out,  the  film  of 
mercury  unites  with  fresh  zinc.     Zinc  is  amalgamated  best  by 


METHODS   OF   ELECTRICAL    STIMULATION         47 

Bring  the  capillary  into  the  field  of  the  micro- 
scope (Leitz  objective  3,  micrometer  ocular),  par- 
allel to  the  micrometer  scale.  The  end  of  the 
tube  should  be  just  visible  at  the  upper  margin 
of  the  field.  If  the  meniscus  is  not  visible,  turn 
the  pressure  screw  slowly  to  the  right  until  the 
meniscus  enters  the  field.  Note  the  position  of 
the  meniscus  on  the  scale.  Close  the  battery  key. 
Let  an  assistant  place  the  metals  in  a  beaker  con- 
taining solution  of  sodium  chloride.  Open  the 
short-circuiting  key  of  the  electrometer. 

When  the  metals  touch  the  electrolyte  a  dif- 
ference in  potential  will  be  set  up,  and  the 
meniscus  will  move  in  the  capillary. 

Note  the  number  of  divisions  of  the  scale 
traversed  by  the  meniscus.  Close  the  electrom- 
eter key.     Wait  several  minutes. 

Now  bring  the  meniscus  back  to  its  original 
position  on  the  scale.     Open  the  electrometer  key. 

The  meniscus  will  move  to  a  much  slighter 
extent  than  when  the  circuit  was  first  made. 

adding  4  per  cent  of  mercury  to  the  molten  zinc  before  casting  ; 
or  the  zinc  may  be  dipped  in  10  per  cent  sulphuric  acid  to  clean 
it,  and  mercury  rubbed  over  the  surface  with  a  brush  or  a  stick 
padded  with  cloth  ;  or  the  zinc  may  be  dipped  in  a  solution 
from  which  the  mercury  will  deposit  on  the  zinc.  Formula  for 
amalgamating  fluid  :  warm  gently  4  parts  mercury  in  5  parts 
concentrated  nitric  acid  and  15  parts  concentrated  hydrochloric 
acid  until  dissolved,  and  then  add  20  parts  more  of  concentrated 
hydrochloric  acid. 


48      GENERAL  PROPERTIES   OF  LIVING   TISSUES 

As  the  displacement  of  the  meniscus  is  propor- 
tional to  the  electromotive  force  of  the  cell,  it  is 
obvious  that  the  latter  has  rapidly  diminished. 
The  solution  contains  the  ions  of  water  as  well 
as  those  of  the  salt.  When  the  circuit  between 
the  platinum  and  zinc  is  completed  the  cations 
H+  and  Na+  move  towards  the  cathode.  There 
the  more  easily  de-ionized  H+  yields  up  its  elec- 
tricity, and  hydrogen  appears  on  the  cathode. 
The  corresponding  quantity  of  electricity  is  con- 
veyed into  the  solution  at  the  anode  by  ioniza- 
tion of  the  zinc.  The  deposition  of  hydrogen 
on  the  negative  plate  checks  the  electromotive 
force  setting  from  the  zinc  to  the  platinum  in 
two  ways :  first,  because  gas  is  a  bad  conductor, 
and  the  effective  surface  of  the  platinum  is 
thereby  diminished  by  the  bubbles  collecting 
on  it ;  and  secondly,  because  hydrogen  is  electro- 
positive, and  creates  an  electromotive  force  in 
the  direction  from  platinum  to  zinc,  and  thus 
"  polarizes "  the  cell.  This  new  electromotive 
force  opposes  the  original  current  from  zinc  to 
platinum. 

The  Daniell  Cell.  —  Daniell  discovered  an  elec- 
tro-chemical method  of  avoiding  polarization,  and 
thus  was  able  to  construct  a  cell  that  would 
furnish  a  current  of  unvarying  strength.  In  the 
Daniell  cell  the  two  metals  employed  are  zinc 


METHODS    OF   ELECTRICAL    STIMULATION        49 

and  copper.  The  amalgamated  zinc  is  placed  in 
a  porous  cup  filled  with  dilute  sulphuric  acid. 
The  copper  is  placed  in  a  solution  of  copper  sul- 
phate kept  saturated  by  crystals  of  the  salt. 
When  the  circuit  is  closed,  the  zinc  "dissolves" 
in  the  sulphuric  acid,  carrying  with  it  the  elec- 
tricity with  which  the  zinc  ions  are  charged. 
The  electricity  is  carried  through  the  solution 
by  the  migration  first  of  hydrogen  and  then  of 


O-x  ,< o-...  ( o 


t 


\ 


\ 


12  3 

Fig.  11  A.  Fig.  11  B. 

A,  earlier  form  of  pole-changer.  The  rubber  handle  prevents  the  cross- 
ing of  the  current  from  one  side  cup  to  the  other.  B,  diagram  of  pole- 
changer  arranged  (1)  to  change  the  direction  of  the  current,  (2)  as  a  double 
key,  without  cross-wires,  (3)  as  a  simple  key. 

copper  ions.  It  leaves  the  solution  at  the  cath- 
ode where  the  copper  ions  are  converted  into 
metallic  copper  and  deposited  on  the  cathode. 
The  quantity  of  zinc  dissolved  and  copper  de- 
posited is  proportional  to  the  quantity  of  the 
current.  One  ampere  deposits  per  minute  19.75 
milligrams  copper,  and  dissolves  20.32  milligrams 

zinc. 

4 


\ 

\ 

\ 
\ 


50      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

It  is  to  be  observed  that  each  metal  is  placed 
in  a  solution  of  its  own  salt.  The  ions  carried  to 
the  respective  poles  are  of  the  same  nature 
chemically  as  the  poles  themselves,  and  hence  do 
not  set  up  opposing  electromotive  forces  when 
they  are  de-ionized. 

The  current  produced  by  the  Daniell  cell  is 
almost  perfectly  constant,  so  long  as  sulphuric 
acid  still  remains  uncombined,  and  so  long  as 
the  sulphate  of  copper  solution  is  kept  saturated. 


Fig.  12.    Rocking  key,  metal  contact ;  about  one-half  the  actual  size. 

It  may  be  remarked  that  the  function  of  the 
porous  cup  is  to  keep  the  copper  from  depositing 
on  the  zinc. 

The  Pole-Changer.1  —  The  instrument  illustrated 
by  Fig.  12  serves  as  a  simple  key,  short-circuiting 
key,  and  pole-changer.     No  mercury  is  used. 

1  Science,  1905,  xxi,  pp.   752-754. 


METHODS  OF  ELECTRICAL  STIMULATION    51 

The  central  binding  posts  are  prolonged  upwards 
and  each  is  slotted  to  receive  a  brass  bar,  which  is 
pivoted  in  the  slot  by  a  horizontal  pin.  The  brass 
bars  are  held  parallel  by  two  rubber  rods  which  serve 
as  handles.  When  the  bars  are  depressed  to  one  side 
or  the  other,  they  engage  between  plates  of  spring 
brass  set  into  brass  blocks,  each  of  which  carries  a 
binding  screw.  Cross-wires  enter  these  blocks,  as 
shown  in  the  figure.  At  one  end  the  cross- wires  are 
soldered  into  the  blocks,  thus  making  an  electrical 
contact.  The  two  blocks  at  the  other  end  are  per- 
forated by  rubber  cores  or  "  bushings  "  through  which 
the  cross-wires  pass.  The  cross-wires,  therefore,  make 
no  electrical  contact  with  these  blocks.  When  a  con- 
tact is  desired,  the  nut  borne  on  the  head  of  each 
cross-wire  is  turned  until  its  face  presses  against  the 
brass  block  outside  the  bushing.  In  this  position  the 
key  serves  as  a  pole-changer,  or  commutator.  When  the 
nut  on  the  cross-bar  between  the  central  posts  is  turned 
until  its  face  presses  against  the  post,  it  will  short- 
circuit  the  central  posts. 

Polarization  Current.  —  Place  two  pieces  of 
platinum  foil  in  a  solution  of  copper  sulphate, 
and  connect  them  to  a  pole-changer  (without 
cross-wires).  Connect  the  remaining  pairs  of 
posts  with  two  dry  cells  in  series  (carbon  of  one 
cell  connected  with  zinc  of  other),  and  with  the 


52      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

0  and  1  metre  posts  of  the  rheochord,  respectively. 
Connect  the  zero  post  and  the  slider  to  the  capil- 
lary electrometer  (Fig.  13).  Turn  the  pole- 
changer  to  pass  the  battery  current  through  the 
copper  sulphate  solution   or  "  electrolyte."     The 

cation  (copper)  will  be 
partially  de-ionized  at 
the  negative  pole,  or 
cathode,  on  which  cop- 
per will  be  deposited 
in  a  fine  film.  The  anion 
(sulphion,  S04)  will  pass 
-~o)  towards  the  positive  pole, 
or  anode,  where  it  gives 
up  its  electric  charge  and 
becomes  the  ordinary  radical  S04.  This  radical 
cannot  exist  uncombined  in  water,  but  forms  sul- 
phuric acid,  setting  free  oxygen,  which  therefore 
appears  at  the  anode. 

The  elements  copper  and  oxygen  deposited 
respectively  on  the  cathode  and  anode  tend  to 
fly  back  into  the  ionic  state ;  and  this  ten- 
dency, taken  in  connection  with  the  opposing 
osmotic  force  of  the  ions  already  in  solution, 
sets  up  an  electromotive  force  equal  to  that 
which  caused  the  de-ionization,  but  in  an  op- 
posite direction.       Hence   the    polarization   cur- 


METHODS    OF   ELECTRICAL   STIMULATION        53 

rent.  On  cutting  off  the  electrolyzing  current, 
the  polarization  current  may  be  measured. 

Note  the  position  of  the  meniscus  of  the  capil- 
lary electrometer.  Turn  the  pole-changer  so  that 
the  cell  is  cut  off  and  the  electrodes  are  brought 
into  the  electrometer  circuit. 

The  meniscus  will  indicate  a  current  opposite 
in  direction  to  the  current  from  the  cell. 

Dry  Cell. — A  "dry"  cell  is  very  convenient 
for  large  classes.  It  usually  consists  of  a  zinc 
cup,  lined  with  plaster  of  Paris,  saturated  with 
ammonium  chloride,  in  the  centre  of  which  'is  a 
carbon  plate  surrounded  with  black  oxide  of 
manganese.  When  the  cell  is  in  action,  the  zinc 
forms  a  double  chloride  of  zinc  and  ammonium 
while  ammonia  gas  and  hydrogen  are  liberated 
at  the  carbon  pole.  These  cells  should  never  be 
used  continuously  for  many  minutes,  for  they  are 
rapidly  polarized  by  the  accumulation  of  hydro- 
gen on  the  carbon  plate.  The  unused  cell  re- 
gains its  difference  of  potential  by  the  union  of 
the  hydrogen  with  the  oxygen  slowly  given  off 
by  the  manganese  dioxide,  which  therefore  acts 
as  a  depolarizer. 

Induction  Currents 

A  most  useful  method  of  electrical  stimulation 
of  living  tissues  is  by  the  induced  current,  and 


54      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

a  clear  idea  of  the  phenomena  of  induction  must 
now  be  gained. 


The  Inductorium *  —  The  primary  coil  of  the  in- 
ductorium  (Fig.  14),  wound  with  double  silk-covered 
wire  of  0.82  mm.  diameter,  having  a  resistance  of  0.5 


Fig.  14.     The  inductorium  ;  one-third  the  actual  size.     (The  set  screw 
holding  the  trunnion  block  tube  against  the  side  rod  is  not  shown.) 


ohm,  is  supported  in  a  head-piece  bearing  three  bind- 
ing posts  and  an  automatic  interrupter.  The  core 
consists  of  about  ninety  pieces  of  shellacked  soft 
iron  wire.  This  core  actuates  the  automatic  inter- 
rupter. The  interrupter  spring  ends  below  in  a  collar 
with  a  set  screw.  By  loosening  the  screw,  the  inter- 
rupter with  its  armature  may  be  moved  nearer  to  or 


1  American  Journal  of  Physiology,  1903,  p.  xxxv. 


METHODS   OF   ELECTRICAL   STIMULATION         55 

farther  from  the  magnetic  core.  Once  set,  the  inter- 
rupter will  begin  to  vibrate  as  soon  as  the  primary 
circuit  is  made.  The  outer  binding  posts  are  used  for 
the  tetanizing  current.  The  left-hand  outer  post  and 
the  middle  post  are  used  when  single  induction  cur- 
rents are  desired ;  they  connect  directly  with  the  ends 
of  the  primary  wire,  thus  excluding  the  interrupter. 
These  several  connections  upon  the  head-piece  are 
simply  arranged  and  are  all  in  view ;  there  are  no  con- 
cealed wires. 

From  the  head-piece  extend  two  parallel  rods  22 
cm.  in  length,  between  which  slides  the  secondary  coil, 
containing  5000  turns  of  silk-covered  wire  0.2  mm.  in 
diameter.  Over  each  layer  of  wire  upon  the  secondary 
spool  is  placed  a  sheet  of  insulating  paper.  Each  end 
of  the  secondary  wire  is  fastened  to  'a  brass  bar 
screwed  to  the  ends  of  the  hard-rubber  spool. 

The  brass  bars  bear  a  trunnion  wrhich  revolves  in 
a  split  brass  block,  the  friction  of  which  is  regulated 
by  a  screw.  The  trunnion  block  is  cast  in  one  piece 
with  a  tube  3  cm.  in  length,  which  slides  upon  the 
side  rods.  A  set  screw,  not  shown  in  Fig.  14,  holds 
the  trunnion  block  tube  and  the  secondary  spool  at 
any  desired  point  upon  the  side  rods.  This  screw 
also  serves  to  make  the  electrical  contact  between  the 
trunnion  block  tube  and  the  side  rod  more  perfect. 
The  secondary  spool  revolves  between  the  side  rods 
in  a  vertical  plane.  When  the  secondary  coil  has 
revolved  through  90°,  a  pin  upon  the  side  bar  of 
the  secondary  coil  strikes  against  the  trunnion  block 


56      GENERAL   PROPERTIES   OF  LIVING   TISSUES 

and  prevents  further  movement  in  that  direction. 
The  right-hand  side  bar  bears  a  half-circle  graduated 
upon  one  side  from  0°  to  90°.  An  index  pointer  is 
fastened  upon  the  trunnion  block.  One  side  rod  is 
graduated  in  centimetres. 

The  side  rods  end  in  the  secondary  binding  posts, 
so  that  moving  the  secondary  coil  does  not  drag  the 
electrodes.  Next  the  binding  posts  is  placed  a  short- 
circuiting  key. 

Magnetic  Induction.  —  Faraday's  experiment. 
Eemove  the  secondary  (larger)  coil  of  the  in- 
ductorium  (Fig.  14)  from  its  slideway  and  con- 
nect its  terminals  with  the  capillary  electrometer. 
Eaise  the  brass  bridge  between  the  binding  posts. 
(If  this  bridge  is  down  its  thick  metallic  mass 
will  offer  such  an  easy  path  between  the  ends  of 
the  secondary  wire  that  nearly  all  —  practically 
all  —  the  electricity  produced  in  this  coil  will 
pass  over  the  bridge,  instead  of  by  the  relatively 
long,  thin  wires  leading  to  the  electrometer.) 
Bring  the  meniscus  into  the  field.  Thrust 
the  north  pole  of  a  magnetized  rod  within  the 
coil. 

The  meniscus  will  move,  indicating  that  an 
electric  current  has  been  induced  in  the  second- 
ary coil.     Note  the  direction  of  the  current. 

Let  the  magnet  remain  in  the  coil. 

The  meniscus  will  return  to  its  former  position. 


METHODS   OF    ELECTRICAL   STIMULATION        57 

Evidently  the  induced  current  is  of  momentary 
duration. 

Withdraw  the  magnet  quickly. 

The  meniscus  will  move  in  the  opposite 
direction. 

Insert  the  south  pole. 

The  induced  current  now  has  the  direction 
opposite  to  that  of  the  current  induced  by  the 
insertion  of  the  north  pole. 

Withdraw  the  magnet  quickly. 

The  induced  current  has  the  direction  opposite 
to  that  of  the  current  induced  by  the  withdrawal 
of  the  north  pole. 

These  results  may  be  thus  expressed :  the 
moving  of  a  magnet  in  the  neighborhood  of  a 
conductor,  or  of  a  conductor  in  the  neighbor- 
hood of  a  magnet,  produces  in  the  conductor  an 
electromotive  force,  which,  on  the  circuit  being 
completed,  creates  a  current  that  would  impart 
to  the  magnet  or  the  conductor  a  movement  in 
the  opposite  direction. 

Magnetic  Field.  Lines  of  Force.  —  The  space 
about  a  magnet  in  which  the  magnetic  forces 
act  is  called  the  "  field  "  of  the  magnet.  If  very 
fine  iron  filings  are  dusted  through  a  muslin 
cloth  onto  a  thin  card  perforated  near  the  centre 
by  a  copper  wire  or  other  conductor,  and  a  strong 
current  is  passed  through  the  wire,  the  filings  will 


58      GENERAL  PROPERTIES   OF  LIVING   TISSUES 

arrange  themselves  in  concentric  circles  around 
the  wire,  particularly  if  the  card  be  gently 
tapped. 

The  position  of  these  "  lines  of  force "  shows 
the  direction  of  the  magnetic  force,  and  their 
number  is  an  index  of  its  intensity. 

To  produce  Electric  Induction,  the  Lines  of 
Magnetic  Force  must  be  cut  by  the  Circuit.  — 
Hold  the  magnet  at  right  angles  to  the  axis  of 
the  coil,  and,  keeping  it  in  this  position,  rapidly 
advance  it  towards  the  coil. 

The  electrometer  will  show  no  current,  because 
the  number  of  the  lines  of  magnetic  force  which 
pass  through  the  field  of  the  conductor  has  not 
been  altered. 

Electro-magnetic  Induction.  — An  electro-magnet 
may  be  used  in  place  of  the  bar  magnet  to  pro- 
duce induction. 

Connect  a  dry  cell  through  a  simple  key  with 
posts  1  and  2  of   the  primary  coil.1    Close   the 

key- 
When  the  current  passes  through  the  primary 

coil,  the  core   of  iron  wire  in  the  coil  will  be 

1  It  will  be  convenient  to  use  the  numbers  1  and  2  to  desig- 
nate the  posts  connected  directly  with  the  ends  of  the  primary 
wire,  excluding  the  vibrating  hammer  ;  the  numbers  2  and  3 
will  indicate  the  posts  that  connect  with  the  ends  of  the  pri- 
mary wire  including  the  hammer.  When  the  battery  is  con- 
nected with  posts  2  and  3  the  hammer  will  vibrate. 


METHODS    OF   ELECTRICAL    STIMULATION         59 

magnetized,  as  is  shown  by  its  attracting  the 
head  of  the  Wagner  hammer. 

Bring  the  meniscus  into  the  field.  Approach  the 
primary  coil  to  the  secondary  as  in  the  experiment 
with  the  magnet.     "Withdraw  the  primary  coil. 

The  electrometer  shows  the  presence  of  in- 
duced currents,  as  before.  These  currents  are 
momentary.  The  first  induction  current  is  in- 
verse, i.  e.  it  runs  round  the  secondary  coil  in  the 
direction  opposite  to  that  taken  by  the  battery  cur- 
rent in  the  primary  coil.  The  second  induced  cur- 
rent is  in  the  same  direction  as  the  primary  current. 

Place  the  coils  at  right  angles  to  each  other. 
Approach  one  towards  the  other. 

No  current  will  be  induced. 

Make  and  break  Induction.  —  Close  and  open 
the  key  in  the  primary  circuit,  thus  making  and 
breaking  the  primary  current. 

The  effect  is  the  same  as  if  the  primary  were 
suddenly  brought  up  to  the  secondary  coil  from 
an  infinite  distance  and  removed  aoain.  The  make 
induction  current  is  in  the  opposite,  the  break  in 
the  same,  direction  as  the  primary  current. 

Turn  the  secondary  coil  on  its  pivot  until  the 
axis  is  at  right  angles  to  the  axis  of  the  primary 
coil.     Make  and  break  the  primary  current. 

No  induction  will  take  place  provided  the 
angle  between  the  coils  is  precisely  90°. 


60      GENERAL  PROPERTIES   OF   LIVING   TISSUES 

On  the  Construction  of  the  Inductorium.  —  Ex- 
amine the  construction  of  the  inductorium.  The 
primary  coil  consists  of  a  few  turns  of  thick  wire. 
More  turns  would  increase  resistance  and  self- 
induction,  —  the  counter  induction  set  up  in  each 
turn  of  the  primary  wire  by  the  passage  of  the 
primary  current  through  neighboring  turns, — 
without  increasing  the  induction  effect  in  the 
secondary  coil. 

The  iron  core  adds  to  the  number  of  lines  of 
magnetic  induction  which  pass  through  the  coils. 
It  has  been  already  shown  (page  58)  that  the 
lines  of  magnetic  induction  produced  by  the  pas- 
sage of  an  electric  current  through  a  wire  are 
closed  circles.  If  the  centre  of  the  coil  were 
filled  with  air,  most  of  these  circles  would  remain 
closed  about  their  own  wire,  for  air  is  not  readily 
permeable  to  magnetism.  But  when  the  iron  core 
is  placed  within  the  coil  the  greater  part  of  the 
magnetic  induction  follows  the  iron  (because  it 
is  more  permeable)  from  end  to  end  of  the  core, 
returning  outside  through  the  air.  Thus  the 
number  of  effective  lines  is  increased.  A  bundle 
of  iron  wires  is  used  instead  of  a  solid  core,  be- 
cause no  induced  current  is  then  possible  through 
the  mass  of  the  iron,  as  would  be  the  case  in  a 
solid  core.  Such  a  current  would  slow  the  speed 
of  magnetization  and  demagnetization. 


METHODS    OF   ELECTRICAL    STIMULATION        61 

The  secondary  coil  is  made  of  many  turns  of 
fine  wire,  because  the  object  of  the  inductorium 
is  to  transform  the  low  electromotive  force  of  the 
cell  into  the  high  electromotive  force  of  the  in- 
duced current.  In  the  induction  coil,  as  in  other 
transformers,  the  electromotive  forces  in  the 
primary  circuit  are  to  those  produced  in  the 
secondary  circuit  approximately  as  the  number 
of  turns  of  wire  in  the  primary  is  to  the  number 
in  the  secondary  circuit. 

If  the  induced  current  is  to  be  passed  through 
conductors  of  low  resistance,  the  high  internal 
resistance  of  the  secondary  coil,  due  to  its  great 
length  of  fine  wire,  will  be  of  importance. 

Place  a  dry  cell  with  simple  key  in  the  pri- 
mary circuit  of  an  inductorium  (posts  1  and  2). 
Connect  the  secondary  coil  with  a  galvanometer. 
Note  the  excursion  of  the  needle  with  a  break 
induction  current.  Eeplace  the  secondary  coil 
with  one  of  fewer  windings  (the  primary  coil  of 
a  second  inductorium  will  serve).  Let  the  dis- 
tance between  primary  and  secondary  coil  be  the 
same  as  before. 

The  excursion  of  the  needle  with  a  break  in- 
duction current  will  be  increased,  or  at  least  not 
proportionately  diminished. 

If,  on  the  other  hand,  the  induced  current  is 
to  be  passed  through  nerve,  muscle,  or  skin,  the 


62      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

resistance  of  the  secondary  coil  will  practically 
be  nothing  in  comparison  with  the  enormons 
resistance  of  animal  tissue. 

Eepeat  the  preceding  experiment,  introducing 
in  the  secondary  circuit  a  high  external  resist- 
ance, i.  e.  a  nerve. 

The  secondary  coil  with  many  turns  of  fine  wire 
now  causes  a  much  greater  deflection  of  the  gal- 
vanometer needle  than  the  coil  with  fewer  turns. 

Interrupter.  —  Instead  of  making  and  break- 
ing the  primary  circuit  by  hand,  an  automatic 
interrupter  is  provided.  The  primary  circuit 
passes  through  a  screw,  the  point  of  which  con- 
veys the  current  through  a  flat  spring  upon 
which  is  mounted  an  iron  disk  opposite  and  near 
to  the  core  of  wire  in  the  primary  coil.  When 
the  current  enters  the  primary  coil,  the  core  is 
magnetized  and  draws  upon  the  iron  disk.  The 
spring,  to  which  the  disk  is  attached,  is  thereby 
drawn  away  from  the  screw-point  through  which 
the  current  is  passing.  Thus  the  current  is 
broken,  and  ceases  to  flow  through  the  primary 
coil ;  the  core  no  longer  is  magnetized,  and  re- 
leases the  iron  disk ;  the  spring  again  makes 
contact  with  the  screw-point,  the  current  is  re- 
established, only  to  be  at  once  again  broken. 
Thus  a  rapid  series  of  make  and  break  induc- 
tion currents  is  secured. 


METHODS    OF   ELECTRICAL    STIMULATION        63 

Draw  a  diagram  of  the  primary  circuit,  indi- 
cating the  connections  of  the  inductorium. 

Empirical  Graduation  of  Inductorium.  —  Con- 
nect the  secondary  coil  with  the  galvanometer. 
Join  the  primary  coil  to  a  dry  cell,  interposing  a 
simple  key.  Turn  the  secondary  coil  on  its  pivot 
until  it  is  at  right  angles  with  the  primary  coil. 
Close  the  circuit. 

The  galvanometer  needle  will  not  swing. 
There  is  no  induced  current.1 

Turn  the  secondary  coil  on  its  pivot,  closing 
the  key  from  time  to  time  to  test  the  induction. 

The  strength  of  the  induction  increases  ap- 
proximately as  the  cosine  of  the  angle  between 
the  coils  increases.  An  empirical  graduation  is 
sometimes  placed  on  a  circular  scale  beneath  the 
coil. 

When  the  axes  of  the  two  coils  lie  in  the  same 
plane,  slide  the  secondary  towards  the  primary, 
making  and  breaking  the  primary  current  from 
time  to  time. 

The  potential  of  the  primary  upon  the  second- 
ary coil,  i.  e.  the  sum  of  the  inductions  of  each 
element  of  the  primary  upon  all  the  elements  of 
the  secondary  coil,  increases  as  the  secondary  is 
brought  nearer  the  primary  coil.  The  increase  is 
not  linear.     As  the  distance  between  the  coils 

1  It  is  difficult  to  place  the  coil  precisely  at  an  angle  of  90.° 


64      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

diminishes,  the  increment  of  increase  in  the  in- 
tensity of  the  induced  current  is  not  the  same 
but  greater  for  each  centimetre  of  approach. 

Graduation.  —  Fasten  a  strip  of  white  gummed 
paper  at  the  side  of  the  base  of  the  inductorium, 
beginning  at  the  end  block  which  holds  the 
primary  coil.  Place  the  secondary  coil  at  the 
end  of  the  slideway.  Make  the  primary  current. 
Kead  the  number  of  degrees  of  deviation  for  the 
break  induction  current  only.  Make  a  line  on 
the  paper  band  exactly  opposite  that  end  of  the 
secondary  coil  which  is  nearer  the  primary. 
When  the  needle  is  again  at  rest,  move  the 
secondary  nearer  the  primary  coil,  and  find  the 
distance  at  which  the  deviation  of  the  needle  in 
response  to  the  break  induction  current  is  n  de- 
grees (for  example,  two)  of  the  scale  larger  than  at 
the  former  position  of  the  coil.  Mark  on  the  white 
strip  the  new  position  of  the  coil.  Continue  in 
this  way  to  find  the  positions  of  the  secondary 
coil  at  which  the  needle  shows  successively  a 
deviation  two  degrees  greater  at  each  new  posi- 
tion, and  mark  them  on  the  paper  band. 

The  marks  on  this  empirical  scale  will  be 
nearer  together  as  the  secondary  approaches  the 
primary  coil.1 

1  The  rough  method  here  employed  serves  merely  to  show 
that  the  increase  in  the  intensity  of  the  induction  current  as 


METHODS    OF    ELECTRICAL    STIMULATION         65 


The  Platinum  Electrodes.  —  The  stimulating  elec- 
trodes are  provided  with  platinum  points  projecting 
about  10  mm.,  polished  hard-rubber  handle,  7.5  cm. 
long,  and  very  flexible  silk-covered  connecting  wires 
65  cm.  long,  ending  in  nickel-plated  brass  tips  (Fig. 
15).  The  rubber  handle  is  in  two  pieces,  screwed 
together,  permitting  easy  access  to  the  connection 
between  the  flexible  wire  and  the 
stiff  wire  into  which  the  platinum 
points  are  inserted. 

The  Flat-jawed  Clamp.  — The 
flat-jawed  clamp,  or  "  Femur 
Clamp"  (Fig.  16),  consists  of 
strong,  smoothly  working  brass 
jaws  attached  to  a  steel  rod. 
The  jaws  are  separated  by  a  spring 
and  brought  together  by  a  screw. 
They  will  hold  objects  of  widely 
varying  size,  —  for  example,  the 
femur  of  a  nerve-muscle  prepara- 
tion or  a  board  a  centimetre  thick.  The  clamp  has  a 
binding  post  for  making  electrical  connection  with  a 
muscle  or  other  conductor  held  between  its  jaws. 

The  Round-jawed  Clamp. —  The  round-jawed  clamp 
is  convenient  for  holding  burettes,  tubing,  rods,  ther- 
mometers, etc.  (Fig.  16). 

The  Double  Clamp.  —  This  is  a  strong  clamp  of 
enamelled  iron  with  two  brass  nickelled  screws  (Fig. 

the  coils  approach  is  not  linear.     An  exact  method  of  gradua- 
tion has  been  given  by  Kronecker. 

5 


Fig.  15.  The  "  platinum  " 
electrodes ;  about  one-third 
the  actual  size. 


66      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

17).  The  screws  move  into  an  angle,  against  the  sides 
of  which  a  large  or  small  rod  may  be  held  firmly  and 
without  sidelash. 

Make  and  Break  Induction  Currents  as  Stimuli. 

—  Make  a  nerve-muscle  preparation.  Connect  a 
dry  cell  with  simple  key  to  the  primary  coil 
(posts   1   and   2).     Fasten   in   the   posts   of   the 


Fig.  16.     The  flat-jawed  clamp  and  the  round-jawed  clamp ;  one-fourth 
the  actual  size. 

secondary  coil  the  stimulation  electrodes,  i.  c. 
the  prolongation  of  the  ends  of  the  secondary 
wire  which  convenience  demands.  Put  the 
secondary  coil  at  the  end  of  the  slide  way  and 

turn  the  coil.      Place  the 

^^_jr~xEE^\  electrode    points    against 

(l^3^^<«QMf   the  nerve.   Open  and  close 

the  primary  circuit. 

Fig.  17.     The  double  clamp,  one-         r¥,,  ,  , 

third  the  actual  si/..  The    muscle   does   not 

contract. 
Move  the  secondary  towards  the  primary  coil, 
opening  and  closing  the  primary  circuit. 


METHODS    OF   ELECTRICAL    STIMULATION         67 

Presently  the  muscle  will  shorten.  (Compare 
pages  175  and  176.)  Observe  that  this  contrac- 
tion was  the  result  of  a  break  induction  current, 
not  a  make. 

Cautiously  move  the  secondary  coil  still  nearer 
the  primary,  making  and  breaking  the  current  as 
before. 

A  point  will  be  reached  at  which  the  make 
induction  also  causes  contraction.  Obviously, 
the  break  current  is  a  stronger  stimulus  than 
the  make  induction  current.  The  cause  of  the 
greater  intensity  of  the  break  induction  current 
lies  in  the  primary  coil.  The  current  which  en- 
ters the  primary  coil  induces  a  current  in  this 
coil  as  well  as  in  the  secondary  coil.  The  direc- 
tion of  this  "self-induced"  current  is  opposite  to 
that  of  the  primary  current,  and  hence  weakens 
it  and  delays  its  development.  The  stimulating 
power  of  electricity  increases  with  both  the  inten- 
sity of  the  current  and  the  quickness  with  which 
the  intensity  alters.  Hence  the  stimulating  power 
of  the  make  induction  current  is  lessened  by  the 
self-induction  of  the  primary  coil.  When,  on 
the  other  hand,  the  primary  circuit  is  broken, 
the  current  stops,  and  although  self-induction 
again  takes  place,  it  cannot  affect  the  primary 
current,  because  the  latter  no  longer  exists.  The 
self-induced  current  at  the  break  of  the  primary 


68      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

current  is  in  the  same  direction  as  the  primary- 
current  before  the  break. 

The  Extra  Currents  at  the  Opening  and  Closing 
of  the  Primary  Current.  —  1.  Be  move  the  secon- 
dary coil  from  the  inductorium.  Connect  posts 
1  and  2  of  the  primary  coil  with  a  dry  cell,  inter- 
posing a  simple  key.  Fasten  the  ends  of  the 
electrode  wires  in  these  same 
^K  ~  posts.     Close  the  primary  cir- 

°)  I  cuit.       Place     the     electrode 

f  <=j=p    "]  points     against    the     tongue. 

\     U     I  Open  the  key. 

^     v0 — =±$f)    J       a    shock    from    the    self- 
^-o^v  y        induced  current  developed  in 

2/  the  primary  coil  will  be  felt. 

Fig.  is.  Draw  a  diagram  of  the  circuits. 

2.  Connect  a  dry  cell  through 
a  key  to  the  metre  posts  of  the  rheochord  (Fig. 
18).  Connect  the  positive  post  and  the  slider  to 
the  primary  coil  of  an  inductorium  arranged  for 
single  induction  currents.  Bring  wires  from  these 
posts  of  the  primary  coil  through  a  simple  key 
to  the  nerve  of  a  nerve-muscle  preparation.  Close 
the  key  in  the  primary  circuit.  Open  and  close 
the  key  in  the  nerve  circuit.  The  muscle  will 
contract  at  closure  and  possibly  at  opening.  By 
means  of  the  slider,  weaken  the  current  through 
the  primary  coil  until  opening  and   closing  the 


METHODS    OF    ELECTRICAL   STIMULATION        69 

key  to  the  nerve  no  longer  produces  contraction. 
Now  let  this  key  remain  closed  and  make  and 
break  the  primary  circuit. 

The  muscle  will  contract  both  on  opening  and 
closure.  The  induction  currents  developed  in 
the  primary  coil  when  the  primary  current  is 
made  and  broken  stimulate  the  nerve,  al- 
though the  galvanic  current  itself  is  powerless 
to  do  so. 

Tetanizing  Currents.  —  Connect  a  dry  cell  to 
posts  2  and  3  of  the  primary  coil.  The  vibrat- 
ing hammer  will  automatically  make  and  break 
the  current.  Place  the  electrodes  against  the 
nerve  or  muscle. 

The  muscle  will  contract  once  for  each  induc- 
tion current,  but  the  contractions  are  so  rapid 
that  they  fuse  into  a  prolonged  shortening  termed 
tetanus. 

Induction  in  Nerves.  —  Faraday  discovered  that 
currents  can  be  induced  in  electrolytes  as  well 
as  in  metallic  conductors.  Induced  currents  may 
therefore  appear  in  nerves  lying  sufficiently  near 
a  primary  circuit. 

Lay  the  well-moistened  nerve  of  a  nerve-muscle 
preparation  around  the  primary  coil  protected  by 
a  piece  of  paraffin  paper  in  such  a  way  that  the 
free  end  of  the  nerve  touches  the  nerve  near  the 
muscle  or  touches  the  muscle  itself,  so  as  to  form 


70      GENERAL   PROPERTIES    OP   LIVING  TISSUES 

a  closed  circuit.  Make  and  break  the  primary 
current. 

Make  and  break  currents  will  be  induced  in 
the  nerve,  and  the  muscle  will  contract. 

Exclusion  of  Make  or  Break  Current.  —  Con- 
nect the  dry  cell  with  posts  1  and  2,  interposing 
a  key.  See  that  the  short-circuiting  key,  i.  e.  the 
thick  brass  bridge  between  the  posts  on  the  sec- 
ondary coil,  is  down.  Connect  the  electrodes 
with  the  secondary  coil,  and  place  their  points 
against  the  nerve  of  a  nerve-muscle  preparation. 
Close  the  primary  key. 

The  muscle  will  not  contract. 

The  resistance  to  the  passage  of  the  induced 
current  through  the  portion  of  nerve  between 
the  ends  of  the  electrodes  is  many  thousand 
times  greater  than  the  resistance  of  the  brass 
bridge  or  short-circuiting  key.  Practically  none 
of  the  electricity  will  pass  through  the  nerve 
when  the  short-circuiting  key  is  closed. 

Open  the  short-circuiting  key  and  then  open 
the  primary  key. 

The  muscle  contracts. 

Eepeat  the  experiment,  letting  the  make  cur- 
rent pass  and  short-circuiting  the  break. 

With  the  primary  key  and  a  short-circuiting 
key  either  break  or  make  induced  currents  can 
be  used  as  stimuli  at  will. 


methods  of  electrical  stimulation      71 

Unipolar  Induction 

1.  Arrange  the  inductorium  for  tetanizing 
currents  (posts  2  and  3).  Make  a  nerve-muscle 
preparation.  Lay  it  on  a  clean  dry  glass  plate. 
Let  the  nerve  rest  on  a  wire  connected  with  one 
pole  of  the  secondary  coil.  Set  the  inductorium 
in  action.  Connect  the  muscle  with  the  earth 
by  touching  the  muscle  with  the  end  of  a  wire 
the  other  end  of  which  rests  on  a  gas  or  water 
pipe. 

The  muscle  will  show  tetanic  contractions, 
provided  the  induced  current  is  sufficiently 
strong.  If  no  tetanus  is  seen,  move  the  second- 
ary coil  completely  over  the  primary. 

Unipolar  induction  may  be  produced  by  the 
electric  currents  in  the  skin.  This  may  be 
demonstrated  with  a  sensitive  nerve-muscle  prep- 
aration. 

2.  Ligature  the  nerve  between  the  electrode 
and  the  muscle,  and  repeat  the  experiment. 

Stimulation  will  still  be  secured.  The  uni- 
polar discharge  passes  through  the  entire  length 
of  nerve  and  muscle  to  or  from  the  point  at 
which  the  connection  with  the  earth  is  made,  and 
thus  stimulates  the  entire  preparation. 

DuBois-Eeymond,  who  was  the  first  to  make 
the    preceding    experiments,   pointed    out    that 


72      GENERAL   PROPERTIES    OF   LIVING  TISSUES 

whenever  the  secondary  circuit  was  open  (i.  e. 
when  the  bridge  between  the  ends  of  the  second- 
ary wire  was  np)  the  making  and  breaking  of 
the  primary  circuit  caused  free  electricity  to 
gather  on  the  ends  of  the  secondary  wire.  When 
the  electro-static  induction  becomes  great  enough 
the  electromotive  force  overcomes  the  resistance 
in  whatever  connecting  path  may  be  offered,  and 
the  electricity  passes  from  the  coil  to  the  earth. 
If  a  part  of  the  path  is  formed  by  irritable 
tissues,  they  will  of  course  be  stimulated. 

3.  The  quantity  of  electricity  passing  through 
the  nerve  may  be  increased  by  approximating 
the  coils  or  by  increasing  the  electrical  capacity 
of  the  conductor,  as  follows :  — 

Eemove  the  wire  connecting  the  preparation 
with  the  gas  pipe.  Set  the  inductorium  in  action. 
Touch  the  muscle  with  the  moistened  finger. 

Contraction  follows. 

Here  the  electrical  capacity  of  the  preparation 
is  increased  by  connecting  the  preparation  with 
the  human  body,  a  conductor  of  large  surface 
(and  through  it  with  the  earth).  A  similar 
result  is  obtained  by  unipolar  stimulation  of 
nerves  and  muscles  while  still  in  the  body  of 
the  animal,  as  in  many  physiological  experi- 
ments. It  is  not  necessary  that  the  surface  of 
the  conductor  be  enormously  large.     The  follow- 


METHODS  OF  ELECTRICAL  STIMULATION   73 

ing  experiment  shows  that  even  very  small  sur- 
faces will  suffice. 

4.  On  a  carefully  dried,  clean  glass  plate  lay 
four  nerve-muscle  preparations.  Let  the  nerve 
of  the  first  rest  on  a  single  wire  the  other  end  of 
which  is  fastened  in  one  of  the  binding  posts  of 
the  secondary  coil.  Place  the  end  of  the  second 
nerve  on  the  tendon  of  the  muscle  of  the  first 
preparation,  the  third  on  the  second  tendon,  and 
the  fourth  nerve  on  the  tendon  of  the  third. 
Eemove  the  secondary  coil  some  distance  (a  few 
centimetres)  from  the  primary,  and  set  the  in- 
ductorium  in  action.  Gradually  approximate 
the  coils. 

As  the  tension  at  the  ends  of  the  secondary 
wire  increases  by  the  approximation  of  the  coils, 
the  first  preparation  will  contract.  On  further 
approximation,  the  first  and  second;  then  the 
first,  second,  and  third ;  and  finally  all  four  will 
contract. 

This  instructive  experiment  shows  that  when 
the  conducting  surface  is  small,  as  in  the  present 
instance,  the  unipolar  action  is  greater  on  the 
parts  nearer  the  secondary  wire  than  on  parts 
farther  away.  The  danger  of  unipolar  action  on 
tissues  lying  near  the  electrodes  in  ordinary 
artificial  stimulation  of  nerves  and  muscles  in 
situ  is  obvious. 


74      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

5.  It  is  not  even  necessary  that  the  conductor 
should  be  actually  in  contact  with  the  prep- 
aration. 

Connect  a  nerve-muscle  preparation,  insulated 
on  a  glass  plate,  with  one  pole  of  the  secondary 
coil,  and  set  the  inductorium  in  action.  The 
secondary  coil  should  completely  cover  the  pri- 
mary. Bring  a  moistened  linger  as  near  the 
muscle  as  possible  without  touching  it. 

With  the  proper  intensity  of  the  primary  cur- 
rent, contraction  will  take  place,  though  absent 
when  the  finger  is  removed. 

The  sudden  approach  of  a  condenser  charged 
with  static  electricity  will  stimulate  an  isolated 
nerve  or  muscle. 

6.  The  danger  of  error  from  unipolar  action  is 
particularly  great  in  electrometer  observations  on 
the  current  of  rest  or  action  current  of  nerve  and 
muscle,  discussed  and  demonstrated  experiment- 
ally in  Part  III,  Chapter  II. 

The  errors  due  to  unipolar  action  can  usually 
be  prevented  by  the  following  precautions :  The 
secondary  coil  should  always  be  connected  with 
the  tissue  to  be  stimulated  through  a  short- 
circuiting  key,  which  should  be  kept  closed  ex- 
cept during  the  intentional  stimulation  of  the 
tissue.  With  this  good  metallic  connection  be- 
tween the  ends  of  the  secondary  wire  there  will 


METHODS   OF   ELECTRICAL    STIMULATION        75 

be  no  static  electrification.  Further,  the  appear- 
ance of  positive  and  negative  electricity  during 
the  period  of  stimulation  must  be  provided 
against,  especially  if  that  period  is  at  all  pro- 
tracted, for  it  must  not  be  forgotten  that  the 
bridge  of  nerve,  which  completes  the  secondary 
circuit  by  uniting  the  two  electrodes,  possesses 
very  high  resistance,  and  thus  affords  but  an 
imperfect  closure  of  the  ends  of  the  secondary 
wire.  This  provision  is  made  by  connecting  the 
positive  electrode  with  the  earth  by  a  good  con- 
ductor, for  example  by  a  copper  wire  leading 
from  the  electrode  to  the  gas  or  water  pipe 
In  case  of  doubt,  a  control  experiment  should 
be  made.  The  nerve  should  be  severed  between 
the  stimulated  point  and  the  muscle,  and  one 
end  laid  on  the  other.  Excitation  through  the 
passage  of  a  nerve  impulse  along  the  nerve  is 
thereby  made  impossible.  If  the  muscle  still 
contracts  when  the  nerve  is  stimulated  above 
the  section,  it  is  because  of  unipolar  stimulation. 

An"  additional  reason  for  care  is  that  the  insu- 
lation of  the  secondary  spiral  is  injured  by  leav- 
ing the  secondary  circuit  open  while  the  hammer 
of  the  inductorium  is  in  action. 

It  may  be  stated  that  the  direction  of  the  uni- 
polar discharge  is  of  importance.  Excitation 
takes  place  only  where  the  positive  charge  enters 


76         GENERAL   PROPERTIES  OF  LIVING  TISSUES 

the   nerve  or  the    negative    charge    leaves   the 
nerve. 

The  break  induction  current  is  more  effective 
than  the  make,  as  the  slower  development  of  the 
latter  causes  the  terminals  of  the  secondary  wire 
to  be  charged  more  slowly  than  by  the  rapidly 
developed  break  current. 

Apparatus. 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Zinc  wire,  4  inches  long.  Copper  wire,  4  inches  long.  Por- 
celain dish.  Mercury.  5  per  cent  sulphuric  acid.  5  per 
cent  solution  of  potassium  chromate.  Iron  wire,  4  inches 
long.  Muscle  clamp.  Iron  stand.  Capillary  electrometer. 
Rheochord.  Microscope  (micrometer  ocular,  objective  3). 
Daniell  cell.  Dry  cell.  Two  platinum  electrodes.  Zinc 
electrode.  Beaker.  Sodium  chloride.  Simple  key.  9 
wires,  2  feet  long.  Saturated  solution  of  copper  sulphate. 
Pole-changer  (in  paper  dish).  Inductorium  (with  elec- 
trodes). Coil  with  few  windings  (primary  coil  of  a 
second  inductorium).  Bar  magnet.  Iron  filings.  Galva- 
nometer. Card,  with  thick  copper  wire.  Ligatures. 
Frogs.  Osmometer  (for  demonstration).  Tradescantia 
discolor.  Serum.  Sodium  chloride  solutions  (0.60,  0.65, 
0.70,  0.75,  0.80  and  5.0  per  cent,  also  0.62,  0.61,  0.60, 
0.59,  0.58,  and  0.57  per  cent).  Microscope.  Defibrinated 
blood.  Twelve  test-tubes.  Tension  indicator.  Soap  solu- 
tion.    Lycopodium.     Alcohol. 


THE    GRAPHIC   METHOD  77 


III 

THE   GRAPHIC   METHOD 

The  studies  next  to  be  undertaken  make  use  of 
the  change  of  form  of  the  contracting  muscle  as 
a  partial  index  to  the  transformation  of  energy 
in  the  tissue.  A  permanent  record  is  desirable. 
Further,  the  changes  in  the  dimensions  of  the 
muscle  are  so  small  that  it  is  necessary  to  have 
the  graphic  record  enlarged,  rather  than  of  actual 
size.  To  satisfy  these  conditions,  the  muscle  is 
attached  near  the  fulcrum  of  a  lever  furnished 
with  a  recording  point.  The  surface  for  the 
writing  is  usually  glazed  paper  which  has  been 
covered  with  a  thin  layer  of  soot  by  passing  the 
paper  through  the  luminous  part  of  a  broad  gas 
flame.  The  paper  is  fastened  (before  smoking) 
on  a  plate  or  on  a  drum  which  moves  past  the 
writing  point,  almost  parallel  to  it,  and  furnishes 
thus  a  continuously  fresh  surface.1 

1  The  paper  is  cut  wider  and  longer  than  the  surface  of  the 
drum.  The  extra  width  is  to  protect  the  bearings  of  the  drum 
from  soot  that  might  otherwise  collect  there  in  smoking  the 


78      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

The  writing  point  rubs  off  the  soot  in  its  path 
and  leaves  a  white  magnified  tracing  of  the 
muscle's  change  in  length  or  whatever  dimen- 
sion is  the  subject  of  record.  The  paper  is  then 
removed,  drawn  through  a  saturated  solution  of 

paper.  The  extra  length  allows  the  edge  of  the  overlap  to  be 
gummed  to  the  paper  below,  permits  the  paper  to  be  removed 
from  the  drum  by  cutting  through  the  overlap  parallel  to  the 
mucilage,  —  the  surface  of  the  drum  being  protected  from  the 
knife  by  the  underlying  paper, — and  provides  an  unsmoked 
surface  by  which  the  paper  can  be  handled  on  its  removal  from 
the  drum.  The  drum  should  be  laid  in  the  centre  of  the  strip 
of  paper,  the  gummed  edge  to  the  left,  and  the  axis  of  the  drum 
precisely  at  right  angles  to  the  long  axis  of  the  paper ;  the 
mucilage  should  be  moistened,  and  the  ends  of  the  paper 
brought  around  and  fastened.  If  the  paper  is  awry,  the  sur- 
face will  not  lie  uniformly  against  the  drum  and  the  record 
will  be  deformed.  The  drum  should  now  be  placed  in  the 
smoking  apparatus,  revolved  uniformly  and  not  too  fast, 
brought  over  the  gas  flame,  lowered  just  below  the  upper  edge 
of  the  flame,  and  covered  with  a  chocolate  brown  layer  of  soot, 
beginning  at  the  operator's  left  hand  and  passing  gradually  to 
the  right.  The  speed  should  be  such  that  one  passage  from 
left  to  right  shall  suffice.  To  trim  the  edges,  hold  the  drum 
in  the  left  hand,  inclined  downwards,  and  pass  a  sharp  knife- 
blade  around  the  lower  edge.  The  handle  of  the  knife  should 
be  kept  lower  than  the  blade,  to  avoid  tearing.  In  removing 
the  paper  from  the  drum,  hold  the  drum  in  the  air  with  the 
left  thumb  pressed  on  the  edge  of  the  paper  near  the  overlap, 
and  cut  through  the  overlapping  edge  near  the  mucilage.  The 
loosened  paper  will  hang  down  and  may  then  be  seized  by  the 
unsmoked  overlap.  In  recording,  let  all  the  curves  begin  near 
the  overlap.  Attention  to  these  details  is  indispensable  to  the 
best  technical  results. 


THE    GRAPHIC    METHOD  79 

white  shellac  in  95  per  cent  alcohol,1  and  hung 
up  until  the  alcohol  is  evaporated.  The  soot 
will  thus  be  coated  over  and  held  in  place  by 
a  thin  layer  of  shellac,  and  the  record  will  be 
secure. 

The  Kymograph.  —  The  improved  kymograph 2 
is  shown  at  the  right  of  Fig.  19,  in  which  it  is  mounted 
as  part  of  the  long  paper  device.  It  consists  of  a 
drum  revolved  by  clockwork  and  also  arranged  to  be 
more  rapidly  revolved  or  "  spun  "  by  hand. 

The  drum  is  of  aluminium,  cast  in  one  piece 
turned  true  in  the  lathe  to  a  circumference  of  50  cm. 
The  height  is  15.5  cm.  The  weight  is  about  600 
grams.  The  drum  slides  upon  a  brass  sleeve  in  bear- 
ings 1.1  cm.  deep  (to  prevent  "sidelash"),  and  is 
held  at  any  desired  height  by  a  spring  clip.  The 
sleeve  ends  in  a  friction  plate,  which  rests  upon  a 
metal  disk  driven  by  the  clockwork.  Sleeve  and 
friction  plate  revolve  about  a  steel  shaft  which  passes 
through  both  the  heavy  plates  containing  the  clock- 
work, and  is  securely  bolted  to  the  bottom  plate. 
The  sleeve  bears  upon  the  steel  shaft  only  by  means 
of  "  bushings  "  at  the  ends  of  the  sleeve,  thus  securing 

1  To  make  this  solution,  the  alcohol  should  be  allowed  to 
stand  on  the  shellac  a  month  or  more  before  using.  A  satisfac- 
tory solution  may  be  made  in  twenty-four  hours  by  dissolving 
375  grams  of  rosin  in  2500  c.c.  of  alcohol. 

2  Introduction  to  Physiology,  1901,  p.  51.  American  Jour- 
nal of  Physiology,  1903,  viii,  p.  xxxvii.  Ibid.,  1904,  x,  p. 
xxxix.     Science,  1906, 


80      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

a  bearing  without  "  sidelash  "  and  with  little  friction. 
As  the  sleeve  with  the  drum  rests  upon  the  friction 
plate  by  gravity  alone,  it  is  easy  to  turn  the  drum  by 
hand  either  forward  or  back,  even  while  the  clock- 
work is  in  action.  At  the  top  of  the  sleeve  is  a  screw 
ending  in  a  point  which,  when  the  screw  is  down, 
bears  upon  the  end  of  the  steel  shaft  and  lifts  the 
sleeve,  and  with  it  the  drum,  until  the  sleeve  no 
longer  bears  upon  the  friction  plate.  The  drum  may 
then  be  "  spun  "  by  hand  about  the  steel  shaft.  The 
impulse  given  by  the  hand  will  cause  the  drum  to 
revolve  for  about  one  minute.  The  speed  during  any 
one  revolution  is  practically  uniform. 

The  clockwork  consists  of  a  stout  spring  about 
6  metres  in  length,  driving  a  chain  of  gears.  The 
speed  is  mainly  determined  by  a  fan  slipped  upon  an 
extension  of  the  last  pinion  shaft  in  the  chain.  Four 
fans  of  different  sizes  are  provided. 

The  speed  is  regulated  by  a  governor  on  the  shaft 
that  carries  the  fan.  When  the  milled  head  shown  to 
the  right  of  the  steel  shaft  in  Fig.  19  is  up,  the  gear 
on  the  extreme  right  of  the  chain  no  longer  engages 
with  the  gear  driven  by  the  spring,  but  runs  "  idle," 
while  the  gear  attached  to  the  friction  plate  engages 
with  the  lower  of  the  two  gears  at  the  left ;  the  pinion 
of  this  lower  left-hand  gear  engages  with  the  spring 
gear.     Fast  speeds  are  then  obtained. 

When  the  milled  head  is  down,  the  gear  attached 
to  the  friction  plate  falls  below  the  left-hand  gear, 
while   the   right-hand    gear  engages   with   the  spring 


THE    GRAPHIC   METHOD  81 

gear  and  through  a  pinion  drives  the  friction-plate 
gear.     Slow  speeds  are  then  obtained. 

These  operations  are  easily  and  rapidly  performed, 
though,  as  in  all  gear  mechanism,  an  instant's  pause 
is  sometimes  required  to  enable  the  gear  teeth  to 
engage.  The  clockwork  should  be  in  motion,  without 
the  fan,  when  the  adjustments  are  being  made. 

With  both  fast  and  slow  gearing  four  fans  of 
different  areas  may  be  used.  They  are  slipped  upon 
an  extension  of  the  last  pinion  shaft  in  the  chain. 
Five  slow  and  five  fast  speeds  (exclusive  of  spinning) 
are  thus  obtained.  An  additional  slow  speed  (50  cm. 
per  hour)  may  be  obtained  with  a  very  large  fan. 
All  speeds  are  regulated  by  a  friction  governor  fast- 
ened to  the  same  shaft  that  carries  the  fan.  With 
one  winding  the  drum  will  revolve  from  about  one 
to  about  seven  hours,  or  longer,  depending  on  the 
fan  employed.    x 

The  Long  Paper  Kymograph.1  —  In  Fig.  19  the 
kymograph  is  arranged  for  use  with  a  sheet  of  smoked 
paper  about  eight  feet  long.  A  rigid  bench  of  steel 
about  97  centimetres  long  firmly  supports  two 
^-shaped  castings  in  which  two  aluminium  drums 
revolve  on  pointed  adjustable  bearings.  One  of  the 
castings  slides  along  the  bench,  and  may  be  fastened 
at  any  desired  distance  from  the  remaining  or  clock- 
work drum,  so  that  paper  from  about  150  to  240 
centimetres  in  length  may  be  stretched  between  the 

Science;,  1906 
6 


82      GENEEAL   FE0PERT1ES    OF   LIVING   TISSUES 


a 


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60 


THE    GRAPHIC    METHOD  83 

drums.  Each  drum  is  provided  with  an  adjusting 
screw,  by  means  of  which  the  drum  may  be  inclined  until 
the  strip  of  paper  is  stretched  uniformly  throughout  its 
height.  This  adjustment  should  preferably  be  made 
upon  the  sliding  drum.  "When  the  adjustment  is 
complete,  the  abscissae  drawn  by  a  writing  lever  in 
successive  revolutions  will  exactly  coincide.  The 
clockwork  drum  does  not  slide  along  the  bench. 
Both  drums  may  readily  be  removed  from  their 
bearings. 

Beneath  the  clockwork  drum  is  a  circular  plate  of 
the  exact  size  of  that  of  the  medium  spring  kymo- 
graph. This  plate  rests  on  two  feet  and  in  fact 
supports  the  anterior  end  of  the  steel  bench.  The 
clockwork  drum  is  driven  by  a  kymograph  in  which 
the  vertical  steel  drum-rod  and  sleeve  are  replaced  by 
a  short  rod  the  top  of  which  is  flush  with  the  upper 
plate  of  the  kymograph.  The  feet  of  this  kymo- 
graph are  hollowed  to  fit  three  rounded  pins.  "When 
the  kymograph  is  set  upon  these  pins,  it  is  at  once 
"  centred "  and  all  side  motion  is  prevented.  A 
coupling  sleeve  is  now  let  down  from  the  shaft  of  the 
clockwork  drum  until  two  projections  on  the  under 
surface  of  the  coupler  engage  with  corresponding 
slots  in  the  kymograph  rod.  The  clockwork  operates 
like  that  of  the  medium-spring  kymograph,  having 
ten  changes  of  speed.  The  speeds  are,  however, 
faster  as  a  stronger  spring  is  used,  the  maximum 
being  about  seven   centimetres  per  second. 

To   smoke    the    paper,    the    coupler    is    raised,   the 


84      GENERAL   PROPERTIES   OF   LIVING  TISSUES 

kymograph  clockwork  is  removed,  and  then  the  entire 
bench  together  with  its  drums  is  placed  horizontally 
in  the    smoker   frame  (Fig.  20). 


Fig.  20.  The  smoker,  showing  the  long  paper  kymograph  in  place.  The 
paper  is  smoked  with  an  oil  lamp  having  a  four  inch  wick.  Near  the 
stand  are  the  handle  with  which  the  drum  is  revolved  to  carry  the  paper 
over  the  lamp  flame,  and  the  two  rods  which  are  inserted  in  the  kymo- 
graph clockwork  when  the  latter  is  used  independently  of  the  long  paper 
arrangement. 

The  graphic  record  involves  the  use  of  appa- 
ratus. It  never  should  be  forgotten  that  the  use 
of  apparatus  always  introduces  more  or  less 
error.  In  every  experiment  the  apparatus 
should  be  criticised  sharply.  The  numerous 
imperfections  which  such  scrutiny  will  bring 
to  light  are  of  two  sorts,  —  the  errors  that  may 
be  neglected,  and  the  errors  that  may  not  be 
neglected  without  seriously  impairing  the  value 
of  the  method  for  the  purpose  in  hand.  For 
example,  a  count  of  the  pulse  rate  with  an  ordi- 
nary watch  will  usually  be  incorrect  by  one  or 


THE   GRAPHIC   METHOD  85 

two  beats  in  the  minute,  but  such  a  record  is 
quite  accurate  enough  for  most  purposes.  The 
use  of  a  stop-watch  marking  fifths  of  seconds 
would  add  nothing  to  the  value  of  the  count, 
for  the  error  introduced  by  numberless  causes 
that  slightly  modify  the  heart-beat  from  minute 
to  minute  is  greater  than  the  error  introduced  by 
using  an  ordinary  watch  instead  of  a  stop-watch. 
The  correction  of  errors  that  are  too  small  to 
alter  essentially  the  value  of  the  method  for 
the  purpose  to  which  it  is  applied  is  usually 
wasteful. 

With  these  points  in  mind,  smoke  a  drum. 
Arrange  the  inductorium  with  simple  key  for 
maximal  break  induction  currents.  Prepare  a 
gastrocnemius  muscle,  fasten  it  in  the  muscle 
clamp,  tie  a  fine  copper  wire  around  the  tendo 
Achillis,  wrap  the  wire  about  the  hook  on  the 
muscle  lever,  and  fasten  the  end  in  the  binding 
post  of  the  muscle  lever  (Fig.  21).  Connect 
the  secondary  coil  with  the  posts  on  the  muscle 
clamp  and  muscle  lever  respectively.  Weight 
the  muscle  with  ten  grams.  Arrange  the  lever 
to  write  on  the  drum.  Eecord  single  contrac- 
tions with  various  speeds. 

Note  that  the  muscle  writes  its  contraction 
in  the  form  of  a  curve,  the  ordinates  of  which 
measure  the  height  to  which  the  load  is  lifted. 


86      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

Light  Muscle  Lever.1  —  A  stout  yoke  (Fig.  21) 
bears  two  set  screws  holding  a  steel  axle  upon  which 
is  mounted  a  light  piece  of  tubing  and  a  hard-rubber 
pulley.  One  end  of  the  tubing  tapers  slightly  to 
receive  the  writing  straw.  The  other  projects  behind 
the  axle,  and  may  be  pressed  upon  by  the  accurately 
cut  after-loading  screw.  The  pulley  is  pierced  with  a 
hole  for  securing  a  fine   wire  by  means  of  which  a 


Fig.  21.     The  light  muscle  lever,  with  double  hook  straw  fastener  ;  the 
actual  size. 


weight  may  be  suspended  from  the  pulley  when 
it  is  desirable  that  the  weight  should  be  applied 
near  the  axis  of  rotation.  The  muscle  may  also  be 
weighted  directly  by  means  of  a  scale-pan  suspended 
from  the  double  hook  to  which  the  lower  end  of  the 
muscle  is  attached.  If  the  tendon  of  the  muscle  be 
fastened  to  the  double  hook  by  a  fine  wire,  the  free 
end  of  the  wire  may  be  carried  to  the  insulated  bind- 

1  First  Catalogue  of  Harvard   Physiological  Apparatus,  Sep- 
tember, 1901. 


THE    GRAPHIC    METHOD  87 

ing  post  provided  for  convenient  electrical  stimula- 
tion. The  upper  end  of  the  muscle  may  be  grasped 
in  the  flat-jawed  clamp  (Fig.  16),  and  thus  connected 
electrically  with  the  binding  post  upon  it. 

In  obtainiug  the  extension  curve  of  muscle  this 
lever,  after-loaded,  may  be  weighted  to  one  hundred 
grams  without  bending  and  thus  deforming  the  curve. 
The  abscissa  will  be  a  straight  line.  The  moving 
parts  are  very  light.  The  apparatus  is  compact  and 
occupies  but  little  of  the  vertical  space  so  valuable 
where  several  recording  instruments  must  be  placed 
upon  the  same  stand. 

Writing  Lever.  —  A  strip  of  aluminium,  bent  at 
one  end  to  fasten  with  the  double  hook,  pointed  at 
the  other,  may  be  used  in  place  of  a  straw. 

Tuning  Fork. — A  nickelled  polished  steel  fork 
(Fig.  22)  with  steel  handle  is  filed  until  it  gives  one 
hundred  double  vibrations  per  second.  The  tuning 
fork  may  be  provided  with  a  paper  or  foil  writing 


Fig.  22.     The  tuning  fork  ;  about  one-sixth  the  actual  size. 

point  and  clamped  to  the  iron  stand.  It  serves  to 
measure  the  latent  period  of  muscular  contraction  and 
similar  phenomena  of  brief  duration. 

Start  the  drum  at  very  rapid  speed.      Bring 
the  writing  point  of  the  vibrating   tuning   fork 


88       GENERAL    PROPERTIES    OF   LIVING   TISSUES 

(Fig.  22)  against  the  paper  below  the  point  of 
the  muscle  lever,  and  stimulate  the  muscle  to 
contract. 

Observe  that  the  tuning  fork  now  gives  the 
time  intervals  on  the  abscissa  of  the  muscle 
curve,  from  which  the  duration  of  the  periods 
of  shortening  and  relaxation  may  be  known. 
Note  also  the  difference  in  appearance  of  curves 
recorded  on  a  slow  and  a  rapidly  moving 
surface. 

Measure  the  interval  between  the  beginning 
of  contraction  and  the  point  of  maximum 
shortening. 

In  your  laboratory  note-book  write  a  critical 
account  of  the  muscle  lever. 

Compare  this  account  with  the  remarks  which 
follow  : — 

The  object  of  the  muscle  lever  is  to  write  a 
magnified  record  of  the  change  in  form  of  the 
muscle.  Usually  the  muscle  is  suspended  in  a 
muscle  clamp  and  its  lower  end  attached  to 
the  lever,  which  then  records  the  shortening  of 
the  muscle.  The  same  lever  may  be  used  to 
record  the  thickening  of  the  muscle ;  in  this 
case  the  muscle  is  of  course  horizontal  and 
the  lever  rests  upon  it.  For  either  purpose 
the  weight  of  the  lever  is  an  objection,  for 
it    tends    to   prevent    the    muscle    from    begin- 


THE   GRAPHIC   METHOD  89 

ning  its  movement  (inertia  of  position).  Once 
in  motion,  the  weight  tends  to  keep  moving, 
and  thus  to  continue  the  record  of  contraction 
after  the  actual  contraction  has  ceased  (inertia 
of  motion).  As  the  inertia  of  motion  increases 
with  the  mass  and  the  square  of  the  velocity, 
the  lighter  the  lever  the  less  the  error.  The 
disposition  of  the  weight  relative  to  the  axis 
is  also  of  importance.  In  a  swinging  system, 
the  nearer  the  mass  to  the  axis  of  rotation,  the 
less  are  the  after  vibrations  or  pendulum-like 
oscillations  which  continue  after  the  original  im- 
pulse has  ceased.  For  this  reason,  in  experi- 
ments likely  to  be  disturbed  by  after  vibrations, 
the  weight  which  the  muscle  lifts  is  attached 
to  the  small  pulley,  so  as  to  be  as  near  the 
axis  as  possible.  In  this  case,  the  weight  on 
the  muscle  is  of  course  not  the  weight  hung  on 
the  pulley;  the  pulley  weight  must  be  divided 
by  the  number  of  times  the  radius  of  the  pulley 
is  contained  in  the  distance  between  the  axis 
and  the  point  of  attachment  of  the  muscle  to  the 
lever. 

It  will  be  observed  that  the  writing  point  is  a 
strip  of  tinsel  bent  slightly  and  placed  parallel 
to  the  writing  surface.  It  is  very  easily  moved 
in  a  direction  at  rio;ht  angles  to  the  writing  sur- 
face,  but  resists  movement  in  a  vertical  direction. 


90      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

The  bend  makes  the  strip  a  weak  spring,  ena- 
bling the  point  to  remain  in  contact  with  the 
drum  throughout  the  excursion  of  the  point  on 
the  paper.  The  writing  point  should  be  as  nearly 
as  possible  parallel  to  the  paper.  Even  in  this 
position,  the  distance  of  the  end  of  the  straw 
from  the  paper  is  necessarily  less  when  the  lever 
is  horizontal  than  when  raised  by  the  contrac- 
tion of  the  muscle,  for  the  end  of  the  lever 
describes  a  curved  line  in  a  plane  tangent  to  the 
recording  surface.  Were  it  not  for  the  spring 
of  the  writing  point,  the  latter  would  leave  the 
drum.  To  remain  on  the  drum  at  the  height  of 
the  contraction,  the  point  must  at  the  beginning 
of  contraction  press  against  the  drum  with  much 
more  friction  than  is  necessary  simply  for  scratch- 
ing through  the  layer  of  soot.  Thus  the  distance 
of  the  writing  point  from  the  axis  is  constantly 
varying,  and  the  magnification  of  the  lever 
is  constantly  changing.  Within  the  limits  ordi- 
narily employed  in  physiology,  the  deformation 
of  the  curve  thereby  produced  is  proportional  to 
the  length  of  the  arc  through  which  the  point 
moves ;  the  curve  should  therefore  be  written 
no  larger  than  is  necessary  for  clearness. 

When  the  smoked  surface  is  at  rest,  and  the 
contracting  muscle  lifts  the  lever,  the  writing 
point  describes  an  arc ;  when  the  muscle  relaxes, 


THE    GRAPHIC   METHOD  91 

the  writing  point  returns  in  the  same  line.  When 
the  drum  revolves,  the  writing  point  describes  a 
curve  as  the  muscle  contracts.  The  maximum 
shortening  of  the  muscle,  or  height  to  which  the 
load  is  lifted,  is  measured  by  a  perpendicular 
drawn  from  the  highest  point  of  the  curve  to  the 
abscissa.  The  time  required  for  the  muscle  to 
reach  this  height,  however,  is  not  the  distance  on 
the  abscissa  from  the  beginning  of  the  curve  to 
the  perpendicular,  but  to  the  point  at  which  the 
segment  of  a  circle  of  a  radius  equal  to  the 
length  of  the  lever  would  cut  the  abscissa  when 
drawn  from  the  highest  point  of  the  curve.  Prac- 
tically, this  measurement  is  made  by  turning  the 
drum  back  until  the  point  of  the  raised  lever 
rests  at  the  summit  of  the  curve,  and  then, 
while  the  drum  is  at  rest,  allowing  the  lever 
to  write  the  ordinate  by  falling  down  to  the 
abscissa. 

Perpendicular  ordinates  may  be  secured  by  a 
long  pin  passed  transversely  through  the  end  of 
the  writing  lever,  and  bent  twice  at  right  angles, 
first  parallel  to  the  paper  and  then  towards  it. 
The  lever  is  perpendicular  to  the  paper  and  very 
near  it ;  the  weight  of  the  pin  keeps  the  point 
against  the  paper  as  the  lever  rises.  The  perpen- 
dicular writing  has  many  faults  in  common  with 
arc  writing. 


92      GENERAL  PROPERTIES   OF  LIVING  TISSUES 


Apparatus 

Normal  saline.  Bowl.  Pipette.  Towel.  Glass  plate. 
Kymograph.  Glazed  paper.  Smoking  apparatus.  Shel- 
lacking trough.  Shellac  in  alcohol.  Muscle  lever  (weight 
pan).  Muscle  clamp.  Stand.  Inductorium.  Electrodes. 
Simple  key.  Dry  cell.  5  Wires.  Fine  copper  wire.  Ten 
gram  weight.     Tuning  fork.     Tin  foil.     Cement.     Frogs. 


STIMULATION    OF    MUSCLE    AND    NERVE  93 


IV 


THE   ELECTRICAL    STIMULATION    OF    MUSCLE 
.     AND   NERVE 

The  Galvanic  Current 

The  study  of  the  changes  occasioned  in  muscle 
and  nerve  by  electrical  stimulation  may  profit- 
ably begin  with  the  action  of  the  galvanic 
current. 

Non-Polarizable  Electrodes.  —  "When  metal 
electrodes  come  in  contact  with  an  electro- 
lyte, polarization  currents  develop  (see  page  51). 
Electrodes  of  metal  for  this  reason  should  be 
avoided  in  the  study  of  the  effect  of  the  galvanic 
current  on  muscle  and  nerve.  A  "non-polar- 
izable  "  electrode  should  be  employed.  Strictly 
speaking,  no  electrode  is  non-polarizable,  but 
practically  the  polarization  errors  are  excluded 
by  the  device  shown  in  Fig.  23. 

The  boot  electrodes  (Fig.  23)  are  made  of  potter's 
clay,  skilfully  fired,  and  are  unglazed.  The  leg  is 
pierced   with    a   hole    28   mm.   deep    and   S   mm.   in 


94      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

diameter,  in  which  is  placed  the  zinc.  The  foot  is 
20  nam.  long,  measured  from  its  junction  with  the 
leg.  In  the  foot  is  a  well  for  normal  saline  solution 
which  shall  keep  the  feet  equally  saturated.  The 
boots  should  ordinarily  be  kept  in  normal  saline  so- 
lution. In  use  the  hollow  leg  of  the  boot  is  half-filled 
with  saturated  solution  of  zinc  sulphate  and  placed  in 
the  clip.  The  well  in  the  foot  of  the  boot  is  now  filled 
with  normal  saline  solution.     If  metal  clips  are  used 


Fig.  23.    Non-polarizable  electrodes  ;  about 
two-fifths  the  actual  size.1 


the  boots  should  be  mounted  on  separate  rods,  to 
prevent  the  current  passing  through  the  unglazed 
boot  to  the  metal  holder  and  thus  to  the  other  boot. 
This  difficulty  is  avoided  by  the  rubber  holders  shown 
in  Fig.  24.  The  electrodes  may  be  mounted  on  a 
brass  rod  called  the  mounting-rod,  or  in  the  moist 
chamber  shown  in  Fig.  24.  The  boot  electrodes 
serve  equally  well  for  leading  off  the  nerve  or  mus- 

1  First  described  in  "  Science,"  1901,  xiv,  pp.  567-570.     The 
well  was  added  in  Nov.  1905. 


STIMULATION    OF   MUSCLE    AND    NERVE 


95 


cle  current  to  the  electrometer  arid  for  stimulation. 
After  use,  the  boots  should  be  emptied,  rinsed  in 
tap  water,  drained,  and  placed  in  several  hundred 
cubic  centimetres  of  normal  saline  solution  until 
wanted  again.  If  the  foot  of  the  hoot  is  kept  saturated 
with  normal  saline  solution  these  electrodes  will  remain 


Fig.  24.     The  moist  chamber  ;  about  three-fifths  the  actual  size. 

non-polarizable.     They  may  also  be  used  with  normal 
saline  clay. 

The  Moist  Chamber.1 — The  moist  chamber  (Fig. 
24)    consists  of  a   porcelain   plate   which    bears    near 

1  Science,  1901,  n.  s.  xiv,  p.  569. 


96       GENERAL    PROPERTIES    OF    LIVING   TISSUES 

the  margin  a  shallow  groove.  In  this  groove  rests  a 
glass  cover  which  for  the  sake  of  clearness  has  been 
omitted  from  the  figure.  To  the  porcelain  plate  is 
screwed  a  rod,  by  which  the  plate  may  be  supported 
on  a  stand.  Within  the  glass  cover  are  two  right- 
angled  rods.  One  of  the  rods  carries  a  small  clamp, 
composed  of  a  split  screw  on  which  moves  a  nut,  by 
means  of  which  the  femur  of  a  nerve-muscle  prepara- 
tion may  be  firmly  grasped.  The  holder  for  the  split 
screw  is  arranged  to  permit  of  motion  in  all  directions. 
Both  right-angled  rods  carry  unpolarizable  electrodes. 
Each  of  these  is  borne  by  a  hard- rubber  holder.  By 
turning  the  leg  of  the  boot  in  the  holder  the  foot  may 
be  brought  as  near  the  foot  of  the  neighboring  elec- 
trode as  may  be  desired.  It  is  desirable  to  mount 
the  boots  on  opposite  rods  as  in  Fig.  24.  A  thick 
wire  of  freshly  amalgamated  zinc,  provided  at  one 
end  with  a  hole  in  which  a  connecting  wire  may  be 
fastened  with  a  set  screw,  is  placed  in  the  leg  of  the 
boot,  and  the  other  end  of  the  connecting  wire 
brought  to  one  of  the  four  binding  posts  shown  in 
Fig.  24.  These  four  posts  are  in  electrical  connec- 
tion with  four  other  posts  beneath  the  porcelain 
plate.  The  air  within  the  moist  chamber  may  be 
kept  saturated  with  water  vapor  by  applying  moist 
filter  paper  to  the  inner  side  of  the  glass  globe. 

Destruction    of    the    Brain    by    Pithing.  —  The 
next  experiment  requires  a  curarized  muscle,  and 


STIMULATION    OF    MUSCLE    AND    NERVE         97 

curarization  is  best  accomplished  by  the  injec- 
tion of  curare  into  the  dorsal  lymph  sac  of  a 
frog  the  brain  of  which  has  been  destroyed. 
Wrap  the  frog  in  the  cloth,  head  out.  Hold  the 
frog  with  the  fingers  of  the  left  hand,  pressing 
down  the  tip  of  the  frog's  nose  with  the  left 
thumb.  Pass  the  right  forefinger  along  the  mid- 
dle line  of  the  head.  A  slight  depression  will  be 
felt  at  the  joining  of  the  skull  and  trunk.  Here 
the  cerebro-spinal  canal  has  no  bony  covering. 
Make  at  this  point  a  cut  about  a  centimetre 
(I  inch)  long  through  the  skin  in  the  middle  line. 
Thrust  the  seeker  vertically  through  the  soft 
tissues  until  the  point  is  stopped  by  the  bony 
vertebrae.  Turn  the  point  of  the  seeker  towards 
the  head,  and  push  it  along  the  brain  cavity, 
moving  it  gently  from  side  to  side. 

Paralysis  of  Voluntary  Motion  by  Curare.  — 
Make  a  very  small  hole  in  the  skin  of  the  back 
into  the  dorsal  lymph  sac.  With  a  fine  glass 
pipette  inject  a  few  drops  of  a  straw-colored 
solution  of  curare.  The  curare  of  commerce  is 
the  dried  juice  of  a  species  of  strychnos.  It  is 
not  a  definite  chemical  compound  and  cannot 
therefore  be  given  in  an  accurate  dose.  It  is 
customary  to  make  a  one  per  cent  solution  of  the 
crude   mass.     This   solution   may  be   kept  from 

7 


98      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

decomposition  by  a  small  crystal  of  thymol.  The 
bottle  should  be  shaken  before  the  curare  is  with- 
drawn. The  curare  should  be  injected  at  the 
beginning  of  the  laboratory  day,  so  that  there 
may  be  time  for  its  action  in  a  dilute  solution. 
The  motor  nerves  are  paralyzed  first  and  the 
effect  should,  if  possible,  be  limited  to  them. 
Strong  solutions  paralyze  other  nerves,  the  heart, 
and  probably  other  muscles. 

Opening  and  closing  Contraction.  —  Place  two 
non-polarizable  boot  electrodes  in  rubber  holders 
upon  a  mounting-rod.  Fill  the  boots  half  full 
of  saturated  solution  of  zinc  sulphate.  Fill  the 
well  in  the  toe  of  each  boot  with  normal  saline 
solution.  Place  well  amalgamated  zincs  in  the 
boots  and  connect  them  through  an  open  simple 
key  with  the  poles  of  a  battery.  Prepare  a 
sartorius  muscle  (Fig.  25)  from  a  curarized  frog,1 
preserving  the  pelvic  and  tibial  attachments. 
Lay  the  muscle  upon  the  toes  of  the  boot 
electrodes.     Close  the  key. 

The  muscle  will  twitch  when  the  current  is 
made  and  probably  when  it  is  broken,  but  during 
the  passage  of  the  current  there  will  be  normally 
no  contraction. 

1  Be  sure  to  cut  off  the  head  or  otherwise  destroy  the  brain 
of  curarized  frogs  before  operating  on  them. 


STIMULATION    OF   MUSCLE   AND    NERVE 


99 


In  frogs  used  during  the  period  of  hibernation 
and  especially  in  those  brought  from  a  cold  store- 
room into  a  warm  laboratory,  the  make  and  some- 
times the  break  of  the  constant  current  may  be 
followed  by  prolonged 
tetanus.  In  such  frogs, 
the  irritability  of  the 
muscles  is  greatly 
increased,  and  the 
changes,  probably 
ionic,  which  occur 
while  the  current  is 
passing  and  after  it  is 
shut  off  are  sufficient  to 
produce  contractions 
not  seen  in  the  normal 
state  (see  page  147). 
Usually  the  muscle  is 
stimulated  only  by  a 
sudden  change  in  the 
intensity  of  the  current. 

Changes  in  Intensity  of  Stimulus.  —  Connect 
one  of  the  electrodes  used  in  the  preceding  ex- 
periment with  one  of  the  poles  of  a  dry  cell. 
From  the  other  pole  lead  a  wire  to  a  bowl  of 
salt  water.  To  the  other  side  of  the  same  bowl 
bring  a  wire  from  the  remaining  electrode. 

When   the  wires   are   slowly  brought   nearer 


e.c. 


t.a. 


Fig.  25.   Hind  limb  of  froj 
view  (Ecker-Wiedersheim). 


anterior 


100      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

together,  there  will  be  no  contraction ;  when  they 
are  brought  quickly  together,  thus  quickly  in- 
creasing the  intensity  of  the  current,  the  muscle 
will  contract. 

With  Indirect  Stimulation.  —  1 .  Smoke  a  drum. 
Make  a  nerve-muscle  preparation  (sciatic  nerve 
and  gastrocnemius  muscle).  Place  the  femur 
in  the  clamp  in  the  moist  chamber.  Let  the 
nerve  rest  on  non-polarizable  electrodes  connected 
through  an  open  key  with  a  dry  cell.  Attach 
the  tendo  Achillis  to  the  muscle  lever.  Let  the 
muscle  lever  write  on  a  slowly  moving  drum. 
Close  and  open  the  key. 

Both  closing  and  opening  contraction  will  be 
seen.  (If  the  frog  has  been  brought  from  a  cold 
room  into  the  warm  laboratory,  opening  and 
closing  tetanus  will  probably  replace  the  usual 
twitch.     See  page  147.) 

2.  Eepeat  the  experiment  on  page  99,  using 
the  nerve-muscle  preparation  instead  of  the 
curarized  muscle. 

It  will  again  be  found  that  the  intensity  of 
the  current  must  be  increased  with  a  certain 
rapidity  in  order  to  stimulate. 

The  experiments  just  made  support  DuBois- 
Reymond's  statement  that  the  electrical  current 
does  not  stimulate  during  the  entire  period  of 
its   flow    through  the   irritable  tissue,  but   only 


STIMULATION   OF   MUSCLE  AND   NERVE       101 

when  the  intensity  is  rapidly  altered  by  making 
or  breaking  the  circuit.  These  experiments, 
however,  were  made  on  the  rapidly  reacting 
skeletal  muscle  of  the  frog.  The  law  does  not 
hold  good  for  sluggish  contractile  tissue.  In- 
deed it  can  be  disproved  even  for  highly  striated 
muscle  by  a  very  careful  examination  of  the 
manner  in  which  excitation  takes  place.  Pfliiger 
discovered  that  when  the  galvanic  current  is 
made,  excitation  takes  place  only  at  the  points 
through  which  the  current  leaves  the  muscle  or 
nerve  (cathodal  stimulation),  and  that  when  the 
current  is  broken,  excitation  takes  place  only 
where  the  current  enters  the  irritable  tissue. 
This  "polar  excitation"  we  must  now  consider. 
We  shall  find,  among  many  other  facts,  the 
refutation  of  the  idea  that  stimulation  does  not 
occur  throughout  the  passage  of  the  current. 

Polar  Stimulation  of  Muscle 

1.  Slit  the  curarized  sartorius  muscle  trouser- 
like  from  the  lower  end.  Lay  each  end  on  a 
boot  electrode.     Make  and  break  the  current. 

On  making  the  current  the  cathodal  side  will 
contract ;  on  breaking,  the  anodal  side. 

2.  Lay  the  muscle  on  ice  covered  with  a  small 
piece  of  paraffin  paper,  to  shield  the  muscle  from 


102      GENERAL   PROPERTIES   OF  LIVING  TISSUES 

water.  When  thoroughly  cold,  place  the  muscle 
in  the  Gaskell  clamp  (Fig.  26),  making  very 
gentle  pressure  across  the  middle,  and  bring  the 
non-polarizable  electrodes  against  the  ends.  Make 
and,  after  a  minute,  break  the  current. 

The  excitation  wave  passes  so  slowly  through 
cooled  muscle  that  the  contraction  can  be  seen 
with  the  unaided  eye  to  begin  at  the  cathode  on 
closing  and  at  the  anode  on  opening  the  circuit. 

3.  Ureter.1  —  Place  the  extirpated  ureter  of 
any  mammal  on  a  glass  plate  set  as  a  cover  on 
a  beaker  containing  hot  normal  saline  solution, 
so  that  the  hot  vapor  of  the  water  shall  keep 
the  ureter  warm.  Bring  the  non-polarizable 
electrodes  against  the  ureter.  Note  which  elec- 
trode is  the  cathode.     Close  the  key. 

After  a  distinct  latent  period  the  ureter  in  the 
cathodal  region,  and  nowhere  else,  will  contract, 
and  the  contraction  wave  will  spread  from  the 
cathode  in  both  directions  along  the  ureter. 

Open  the  key. 

The  Gaskell  Clamp.  —  The  tapered  edge  of  a  hard- 
rubber  block  is  brought  against  a  similar  edge  by 
means  of  a  fine  screw  (Fig.  20).  With  this  clamp 
the  heart  muscle  may  be  compressed,  after  GaskelFs 

1  The  experiment  succeeds  also  with  extirpated  pieces  of  in- 
testine :ili"iit  lour  iii<hcs  long,  provided  they  are  kept  warm 
with  normal  saline  solution. 


STIMULATION   OF   MUSCLE   AND   NERVE       103 

method,   until  conduction  between  auricle   and  ven- 
tricle is  partially  or  wholly  interrupted.     The  clamp 


Fig.  26.    The  Gaskell  clamp  j  about  one-third  the  actual  size.1 

is  also  used  to  press  upon  the  sartorius  until  the  con- 
duction wave  is  blocked  while  the  excitation  wave 
still  passes. 

The  contraction  takes  place  now  only  at 
the  anode,  and  the  contraction  wave  spreads 
from  that  point  over  the  muscle  (as  making 
the  current  is  a  less  effective  stimulus  than 
breaking  it  may  be  necessary  to  increase  the 
strength  of  the  current,  or  to  keep  it  closed  a 
considerable  time,  in  order  to  secure  making 
contraction). 

4.  Intestine.  —  Place  the  non-polarizable  anode 
on  the  intestine  of  a  freshly  killed  rabbit  or  frog, 
the  cathode  on  some  indifferent  point,  for  example 
the  liver.     Close  the  key. 

The  intestine  will  constrict  in  the  anodal  re- 
gion and  remain  constricted  during  the  passage 
of  the  current,  provided  it  be  not  so  long  as  to 

1  This  form  was  first  described  in  the  Catalogue  of  the  Harvard 
Apparatus  Company,  May.  1905. 


104      GENERAL  PROPERTIES   OF   LIVING  TISSUES 

cause  fatigue.  A  peristaltic  contraction  wave 
usually  passes  from  the  anode  in  both  directions 
along  the  intestine. 

Place  the  cathode  on  the  intestine,  and  the 
anode  on  an  indifferent  point.     Close  the  key. 

A  small,  indistinct  thickening  will  be  seen  in 
the  cathodal  region. 

Thus  the  intestine,  while  it  serves  admirably  to 
illustrate  a  polar  action  of  the  galvanic  current,  ap- 
parently differs  from  the  tissues  already  considered 
in  that  closure  causes  contraction  at  the  anode  in- 
stead of  the  cathode.  The  exception  is  only  appar- 
ent, and  its  explanation  is  that  the  point  at  which 
the  electrode  touches  the  peritoneal  surface  of  the 
many-layered  intestinal  wall  is  not  the  physiologi- 
cal anode  or  cathode ;  i.  e.  not  the  point  at  which 
the  current  actually  enters  or  leaves  the  muscular 
coat.     This  matter  is  discussed  on  page  110. 

5.  Smoke  a  drum.  Eaise  the  drum  off  the  fric- 
tion bearing  by  turning  the  screw  at  the  top  of  the 
shaft  to  the  right.  Arrange  two  muscle  levers  1 
and  the  electro-magnetic  signal  (Fig.  27)  to  write 
on  the  drum  in  the  same  vertical  line.  Place  the 
electro-magnetic  signal,  together  with  a  simple 
key,  in  the  circuit  between  one  dry  cell  and  the 
rheochord.  Bring  the  slider  near  the  positive 
post  of  the  rheochord. 

1  Or  heart  levers  (Fig.  53,  page  311). 


STIMULATION    OF   MUSCLE    AND   NERVE        105 


Fig.  27.    The  signal  magnet ;  the  actual  size. 

The  Electro-magnetic  signal.1  —  A  protecting  metal 
box  (Fig.  27),  open  at  the  front  and  ends,  contains  a 
strong  magnet,  the  armature  of  which  is  mounted  upon 
a  steel  spring.  An  accurate  fine  adjustment  screw  reg- 
ulates the  excursion  of  the  armature.  One  binding 
post  is  mounted  upon  the  metal  box,  the  other  is  insu- 
lated by  a  rubber  block.  This  signal,  in  circuit  with  a 
vibrating  tuning  fork,  will  record  one  hundred  double 
vibrations  per  second.  In  the  primary  circuit  of  the 
inductorium  it  will  record  the  make  and  break  of  the 
current  without  after-vibrations  which  are  prevented  by 
lead  foil  placed  on  the  spring  where  it  strikes  the  limit- 
ing screw.  Residual  magnetism  is  obviated  by  parch- 
ment paper,  fastened  to  the  spring  with  shellac  at  the 
point  where  the  spring  would  touch  the  core  of  the 
magnet.  The  handle  is  long  enough  to  bring  the  writ- 
ing point  directly  above  or  below  the  writing  point  of 
the  muscle  lever  clamped  to  the  same  iron  stand. 

The  metal  box  is  of  soft  iron  and  serves  as  an 
extension  of  the  magnet  core,  thus  completing  the 
magnetic  circuit,  and  doing  away  with  a  second  spool. 
The  magnetic  power  is  further  improved  by  boring 
out  the  core,  which  is  then  "  softened  "  by  heat. 

1  First  Catalogue  of  Harvard  Apparatus,  September,  1901,  p.  46. 


106      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

Fasten  a  curarized  sartorius  muscle  by  the  middle 
in  the  Gaskell  clamp ;  the  pressure  should  be 
enough  to  prevent  the  contraction  wave  of  one 
part  reaching  the  other  part,  but  not  great  enough 
to  prevent  the  passage  of  the  excitation.  Place 
the  muscle  vertical  to  the  writing  levers.  Tie  a 
thread  around  the  pelvic  and  tibial  fragments 
and  fasten  each  thread  to  a  muscle  lever,  so  that 
each  half  of  the  muscle  may  record  its  contrac- 
tion independently  of  the  other.  Moisten  two 
strands  of  lamp  wick  with  normal  saline  clay. 
Tie  one  strand  around  each  end  of  the  muscle 
and  lay  the  free  portion  of  the  strands  on  the 
toes  of  boot  electrodes  properly  mounted.  Note 
which  lever  is  connected  with  the  cathodal  end. 
Make  the  current.  If  the  muscle  does  not  con- 
tract, move  the  slider  along  the  wire  a  short  dis- 
tance towards  the  positive  post  (so  as  to  bring 
a  stronger  current  through  the  electrodes)  and 
make  the  current  again.  When  both  make  and 
break  contractions  are  secured,  see  that  the  writ- 
ing points  record  properly,  and  "  spin  "  the  drum, 
but  not  too  fast.  As  soon  as  the  drum  moves 
steadily,  make  and  then  break  the  current. 

The  moment  of  making  and  breaking  the  cur- 
rent will  be  recorded  by  the  electro-magnetic 
signal.  An  instant  later  the  muscle  levers  will 
begin  their  record  of  the  contractions. 


STIMULATION   OF   MUSCLE   AND   NERVE      107 

It  will  be  found  that  the  cathodal  half  of 
the  muscle  contracts  first  on  closing,  the  anodal 
half  on  opening  the  circuit.  Evidently  the 
excitation  began  on  closure  at  the  cathode  and 
passed  thence  to  the  anode,  while  on  opening 
the  circuit  the  excitation  began  at  the  anode 
and  passed  to  the  cathode. 

In  order  to  measure  this  interval  accurately 
the  drum  should  be  turned  back  until  the  writ- 
ing point  of  the  signal  lies  precisely  in  the  ordi- 
nate drawn  by  it  during  the  experiment.  The 
muscle  should  then  be  stimulated.  The  ordinate 
now  drawn  by  the  muscle  with  the  drum  thus 
at  rest  will  be  synchronous  with  that  drawn  by 
the  signal  during  the  experiment,  and  will  mark 
upon  the  abscissa  of  the  muscle  curve  the  moment 
of  stimulation, 

6.  Tonic  Contraction.  —  Connect  a  dry  cell 
through  an  open  simple  key  with  the  metre 
posts  of  the  rheochord.  Connect  non-polarizable 
electrodes  with  the  positive  post  and  the  slider. 
Fasten  one  end  of  the  curarized  sartorius  (pre- 
pared with  fragments  of  pelvis  and  tibia  attached) 
in  the  muscle  clamp.  Tie  a  thread  to  the  other 
end  and  fasten  the  thread  to  the  upright  pin  of 
the  muscle  lever.  Let  non-polarizable  electrodes 
rest  on  the  muscle  near  the  respective  ends. 
Use  a  strength  of  current  that  will  just  cause 


108      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

contraction  on  closure.  Watch  very  closely  the 
cathodal  region  near  the  junction  of  the  muscle 
fibres  with  the  tendon.     Close  the  key. 

After  the  closing  contraction,  the  ends  of  the 
muscle  fibres  next  the  tendon  in  the  cathodal 
region  will  show  a  faint  but  distinct  thickening, 
which  will  remain  until  the  current  is  broken. 

These  several  experiments  demonstrate  that  in 
galvanic  stimulation  of  both  skeletal  and  smooth 
muscle  the  excitation  takes  place  at  the  points 
where  the  current  leaves  and  enters  the  muscle. 
Before  inquiring  whether  this  law  holds  good  for 
the  heart,  the  muscle  cells  in  which  have  a  form 
intermediate  between  the  smooth  muscle  cell  and 
the  cells  of  skeletal  muscle,  it  will  be  necessary 
to  consider  whether  the  points  of  contact  with 
the  electrodes  are  always  the  real  anode  and 
cathode. 

Physiological  Anode  and  Cathode.  —  When  the 
electrodes  are  placed  directly  on  a  nerve,  or  are 
applied  to  a  muscle  with  straight  parallel  fibres  in 
such  a  way  that  the  current  flows  through  each 
fibre  from  end  to  end,  the  anode  and  cathode 
obviously  coincide  with  the  points  at  which  the 
electrodes  touch  the  muscle.  When,  however, 
the  fibres  are  of  irregular  shape,  or  are  irregularly 
disposed,  the  current  lines  can  no  longer  traverse 
the   fibres  from  end  to  end,  but  will  enter  and 


STIMULATION    OF   MUSCLE   AND    NERVE        109 

leave  fibres  at  points  other  than  those  in  contact 
with  the  electrodes. 

The  difference  between  the  operator's  elec- 
trodes and  the  physiological  anode  and  cathode 
is  also  obvious  when  the  electrodes  are  applied 
to  skin,  connective  tissue,  mucous  membrane,  etc., 
covering  the  muscle  or  nerve,  —  the  points  at 
which  the  electrodes  touch  the  covering  tissue 
cannot  be  the  points  at  which  the  current  actu- 
ally leaves  or  enters  the  muscle. 

The  failure  to  keep  this  distinction  in  mind 
may  lead  to  wholly  erroneous  interpretations. 
Thus  when  the  ureter  is  extirpated,  or  is  raised 
from  the  tissues  on  which  it  normally  rests,  its 
reaction  to  the  galvanic  current  follows  the  law, 
—  contraction  begins  at  cathode  on  making,  at 
anode  on  breaking  the  current;  but  when  the 
ureter  is  stimulated  in  situ,  exactly  the  opposite 
effect  is  seen,  —  contraction  begins  at  anode  on 
making  the  current.  The  explanation  is  that 
the  current  lines  in  the  latter  case  are  very 
widely  diffused  through  the  conducting  tissues 
on  which  the  ureter  lies,  so  that  the  current 
passes  into  and  out  of  the  muscle  fibres  for  some 
distance  either  side  of  the  positive  electrode. 
Each  point  at  which  the  current  leaves  a  fibre 
is  a  secondary  cathode,  and  if  the  number  of 
such  points   is  large,  cathodal  stimulation  will 


110       GENERAL   PROPERTIES    OF   LIVING   TISSUES 

take  place  in  what,  superficially  regarded,  is  the 
anodal  region  (compare  page  131,  and  Fig.  37). 
The  same  explanation  holds  good  for  the  intes- 
tine (see  page  103).  The  formation  of  physio- 
logical anodes  and  cathodes  is  well  shown  in  the 
next  experiment. 

Physiological  Anodes  and  Cathodes  in  Bechis 
Muscle.  —  Eemove  the  rectus  abdominis  muscle, 
from  a  curarized  frog.  Note  the  tendinous  cross 
bands  which  divide  the  muscle  from  side  to 
side  and  divide  it  into  parts.  Lay  the  muscle 
smoothly  on  a  glass  slide.  Connect  the  non- 
polarizable  electrodes  through  a  simple  key  with 
a  dry  cell.  Place  one  electrode  on  each  end  of 
the  muscle.     Close  the  key. 

On  closure,  the  cathodal  side  of  each  division 
of  the  muscle  will  show  a  sharply  defined  con- 
tinued contraction  of  the  ends  of  the  fibres  at 
their  insertion  in  the  transverse  tendinous  bands. 
On  opening,  the  cathodal  contraction  disappears, 
and  a  similar  thickening  of  the  fibres  is  seen  at 
the  anodal  side  of  each  division.  The  twitch  of 
each  segment  on  closure  and  opening  of  the  cur- 
rent also  starts  respectively  from  the  cathodal 
and  anodal  ends  of  each  segment.  These  effects 
are  best  seen  through  a  magnifying  glass. 

Polar  Stimulation  in  Heart.  —  The  muscle  cells 
of  the  heart  are  not  only  of  irregular  shape,  but 


STIMULATION  OF  MUSCLE  AND  NERVE   111 

they  are  so  joined  with  each  other  as  to  make  it 
impossible  to  pass  a  current  through  the  heart 
muscle  without  the  current  lines  cutting  fibres 
in  every  direction.  It  would  seem  therefore  that 
secondary  anodes  and  cathodes  would  be  formed 
to  such  a  degree  that  the  demonstration  of  polar 
excitation  would  be  difficult  or  impossible.  Ex- 
perimentation shows  however  that  this  is  not  the 
case.  The  heart  behaves  like  a  single  hollow 
fibre. 

Monopolar  Method.  —  The  small  size  and  conical 
form  of  the  ventricle  of  the  frog's  heart  make  the 
ordinary  method  of  stimulation,  in  which  the 
electrodes  would  both  be  placed  on  the  heart, 
less  suitable  than  the  monopolar  method.  This 
method  was  suggested  by  the  fact  that  the 
stimulating  effect  of  the  galvanic  current  depends 
on  its  density.  If  one  electrode  has  a  large  sur- 
face, and  the  other  a  very  small  surface,  the 
current  lines  will  be  distributed  through  a  con- 
siderable cross-section  in  the  first  instance  and 
converge  to  a  small  cone  in  the  second.  The 
threshold  value  of  stimulation  will  not  be 
reached  at  the  large  electrode,  and  stimulation 
will  occur  only  at  the  small  electrode.  Thus  the 
large  "indifferent"  electrode  may  be  placed  on 
any  part  of  the  frog's  body,  and  the  convenient 
small  electrode  be  used  to  stimulate  the  heart 


112       GENERAL   PROPERTIES    OF   LIVING    TISSUES 


Cover  the  indifferent  electrode  (consisting  of  a 
brass  plate  furnished  with  a  binding  post)  with 
cotton  wet  with  saline  solution.  Mount  a  non- 
polarizable  boot  electrode.  Con- 
nect a  dry  cell  with  the  metre 
posts  (0  and  1)  of  the  rheochord 
through  a  simple  key  (Fig.  28). 
Connect  post  0  and  the  slider 
through  a  pole-changer  (with 
cross-wires)  with  the  electrodes. 
Expose  the  heart,  according 
to  the  following  method  : 
brainless  frog,  back  down,  in  the 
holder  (Fig.  29).  Cut  through  the  skin  across 
the  middle  of  the  body  from  side  to  side. 
Make  a  second  cut  in  the  middle  line  from  the 


Fig.  28 

Place    the 


Fig.  29.     The  frog  board,  with  spring  clips  ;  about  one-fourth  the  actual 


first  cut  to  near  the  lower  jaw.  Turn  back  the 
flaps.  Cut  through  the  sternal  cartilage  near  its 
lower   end,   thus    avoiding    the   epigastric   vein. 


STIMULATION    OF   MUSCLE    AND   NERVE       113 

Cautiously  remove  the  breast  bone,  doing  no 
harm  to  deeper  parts.  Open  the  delicate  mem- 
brane (pericardium)  which  surrounds  the  heart. 
Tie  a  ligature  about  the  sinus-auricular  junction, 
to  stop  the  ventricular  contractions.  Place  the 
indifferent  electrode  over  the  larynx  and  the  non- 
polarizable  electrode  on  the  ventricle.  Turn  the 
pole-changer  so  that  the  electrode  on  the  heart 
becomes  the  anode.  Close  and  then  open  the 
key. 

Contraction  will  take  place  on  opening  only, 
if  at  all.  Eeverse  the  pole-changer  so  that  the 
cardiac  electrode  becomes  the  cathode.  Close 
and  then  open  the  key. 

Contraction  takes  place  at  closure  only. 

Polar  Stimulation  of  Nerve 

Law  of  Contraction.  —  1.  Whether  contraction 
will  follow  the  galvanic  stimulation  of  a  motor 

O 

nerve  depends  on  the  irritability  of  the  nerve 
and  the  direction  and  intensity  of  the  current. 
The  current  may  pass  through  the  intrapolar 
portion  of  the  nerve  towards  the  muscle  (de- 
scending current)  or  away  from  it  (ascending 
current).  The  intensity  may  be  weak,  medium, 
or  strong ;  intensity  in  this  case  is  evidently 
merely  a  relative  term,  depending  on  the  irrita- 


114      GENERAL   PROPERTIES   OF   LIVING  TISSUES 

bility  of  the  particular  nerve  in  hand.     We  will 
test  first  the  effect  of  the  ascending  current. 

Connect  a  dry  cell  through  an  open  key  with 
the  metre  posts  of  the  rheochord  (Fig.  30).  Join 
the  positive  post  and  the  slider  through  a  pole- 
changer  (cross-wires  in  place),  with  the  non- 
polarizable     electrodes     placed     in     the     moist 


Fig.  30. 


chamber  (Fig.  24,  page  95),  in  the  holders  farthest 
from  the  opening  for  the  muscle.  Make  a 
nerve-muscle  preparation.  Secure  the  femur  in 
the  femur  clamp  of  the  moist  chamber.  Let 
the  nerve  lie  on  the  non-polarizable  electrodes. 
Attach  the  Achilles  tendon  to  the  muscle  lever. 
Keep  the  air  in  the  chamber  moist  by  lining 
the  glass  shade  with  filter  paper  saturated  with 
water.     Arrange    the   pole-changer   so   that   the 

1  The  inductorium  shown  in  Fig.  30  is  not  used  in  this  ex- 
periment, but  in  the  first  experiment  on  page  116. 


STIMULATION    OF    MUSCLE   AND    NEEVE       115 

anode  shall  be  next  the  muscle.  Move  the  slider 
near  the  positive  post.  Make  and  break  the  gal- 
vanic current.  If  no  contraction  is  secured, 
move  the  slider  to  increase  the  current,  and 
repeat  the  experiment. 

The  first  contraction  will  take  place  on  mak- 
ing the  current.  Continue  to  increase  the  cur- 
rent strength  by  moving  the  slider. 

A  point  will  be  reached  at  which  contraction 
will  occur  both  on  opening  and  closure. 

Increase  the  intensity  of  the  current  by  add- 
ing dry  cells  in  series  (zinc  to  carbon),  testing 
the  effect  after  each  addition  by  closing  and 
opening  the  current. 

An  intensity  will  be  reached  at  which  opening 
and  not  closure  causes  contraction. 

In  a  similar  manner,  work  out  the  law  of  con- 
traction for  descending  currents.  (It  may  be 
necessary  to  take  a  fresh  nerve-muscle  prepa- 
ration.) 

Set  down  the  results  in  a  table. 


Intensity 

Ascending 

current. 

Descending  current. 

of  current. 

Make. 

Break. 

Make.                Break. 

Weak. 

Contr. 

Rest. 

Contr.     Rest. 

Medium. 

Contr. 

Contr. 

Contr.     Contr. 

Strong. 

Rest. 

Contr. 

Contr.     Rest  (Weak  contr.) 

2.   The  remarkable  nature  of  these  results  is 
apparent  on  observing  that  contraction  is  easily 


116      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

secured  on  closing  a  weak  ascending  current  and 
yet  cannot  be  obtained  with  a  strong  one.  The 
first  step  in  the  inquiry  into  the  causes  of  the 
phenomena  is  to  determine  whether  the  stimu- 
lation is  polar.  That  the  nerve  impulse  really 
starts  at  the  cathode  on  closure  and  at  the  anode 
on  opening  is  shown  (1)  by  the  fact  that  the 
interval  between  stimulation  and  contraction, 
with  the  ascending  current,  in  which  the  anode 
is  next  the  muscle,  is  longer  at  closure  than  on 
opening,  while  the  opposite  is  the  case  when  the 
current  is  descending.  (2)  With  descending 
currents,  it  sometimes  happens  that  opening 
produces  tetanus  instead  of  a  simple  twitch. 
If  this  tetanus  appears,  the  student  should  sever 
the  nerve  between  the  electrodes.  Immediately 
the  contractions  will  cease.  They  must  there- 
fore have  arisen  at  the  anode,  for  the  cathode 
still  remains  in  full  connection  with  the  muscle. 

Changes  in  Irritability.  —  The  second  step  in 
this  inquiry  is  to  determine  the  nature  of  the 
changes  at  the  poles.  For  this  purpose  the 
nerve  should  be  stimulated  in  the  cathodal  and 
anodal  regions  during  the  passage  of  the  constant 
current. 

1.  Pass  two  needles  through  a  cork  placed  in 
the  rubber  holder  next  the  muscle  in  the  moist 
chamber.     Connect  them  with  the  secondary  coil 


STIMULATION   OF  MUSCLE  AND   NERVE    '  117 

of  an  inductorium  (Fig.  30).  Arrange  the  pri- 
mary for  single  induction  shocks,  which  must 
not  be  maximal.  Turn  the  pole-changer  to  bring 
the  cathode  next  the  metal  electrodes.  Using  a 
weak  induction  current  as  stimulus,  record  on  a 
stationary  drum  three  contractions:  (1)  before 
the  passing  of  the  galvanic  current  through 
the  nerve,  (2)  during  its  passage,  (3)  after  its 
passage. 

The  second  contraction  —  that  obtained  by 
stimulating  in  the  cathodal  region  during  the 
passage  of  the  galvanic  current  —  will  be  greater 
than  the  other  two. 

Eeverse  the  galvanic  current  and  repeat  the 
experiment,  the  stimulation  now  being  in  the 
anodal  region. 

The  stimulation  in  the  anodal  region  during 
the  passage  of  the  galvanic  current  causes  less 
than  the  normal  contraction. 

2.  The  stimulating  current  may  be  superposed 
directly  on  the  polarizing  current  by  using  the 
same  electrodes. 

Connect  a  dry  cell  through  an  open  key  with 
the  0  and  1  metre  posts  of  the  rheochord 
(Fig.  31).  Connect  the  positive  post  of  the 
rheochord  with  one  of  the  non-polarizable  elec- 
trodes. Join  the  slider  to  one  end  of  the  second- 
ary  wire  of   an   inductorium ;  to  the   other  end 


Fig.  31. 


118      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

join  the  remaining  non-polarizable  electrode.  If 
the  positive  pole  of  the  secondary  coil  is  not 
known,  determine  it  by  the  electrolytic  method 
(page   158).     Arrange   the  primary  coil  of   the 

inductorium  for  single 

====*wp\  submaximal  induction 

/\2^\  jj        \]  currents.     Make  and 

Vo^o  ^jw  (^.Culi  |  break    the    induction 

f ?       =      sf  j  current,    and    record 

v*/\»-^  /  the    contractions    on 

the  drum.  Now  pass 
a  weak  polarizing  cur- 
rent through  the  nerve  and  stimulate  again  with 
the  induction  current. 

It  will  be  found  that  the  stimulating  effect  of 
the  induction  current  is  increased  when  the 
direction  of  the  induction  current  coincides  with 
that  of  the  polarizing  current,  i.  e.  when  the 
cathode  (which  is  the  sole  source  of  the  induc- 
tion stimulus,  as  pointed  out  on  page  160)  coin- 
cides with  the  cathode  of  the  polarizing  current. 
When  the  cathode  of  the  induction  circuit  falls 
in  the  anodal  region  of  the  polarizing  circuit,  the 
stimulating  effect  is  diminished.  Very  strong 
polarizing  currents  produce  such  alterations  in 
irritability  that  the  additional  alteration  caused 
by  the  brief  induction  current  is  not  great  enough 
to  be  a  stimulus. 


STIMULATION   OF  MUSCLE   AND   NERVE      119 

The  law  revealed  by  this  experiment  may  be 
thus  expressed.  The  same  stimulating  current 
has  a  greater  stimulating  effect  when  it  coincides 
in  direction  with  a  pre-existing  current,  and  a 
lessened  effect  when  it  is  opposed  in  direction  to 
a  pre-existing  current.  This  law  explains  the 
interference  observed  between  stimulating  cur- 
rents and  demarcation  or  injury  currents  of  nerve 
and  muscle  (see  page  292). 

3.  Place  a  drop  of  saturated  solution  of  sodium 
chloride  on  the  nerve  in  the  extrapolar  region 
near  one  of  the  non-polarizable  electrodes. 
Eecord  the  irregular  tetanus  (chemical  stimu- 
lation) on  a  slowly  moving  drum.  Make  the 
polarizing  current. 

Note  that  the  tetanus  is  increased  when  the 
cathode  is  nearer  the  stimulating  solution,  but 
diminished  when  the  anode  is  nearer. 

Hence  the  irritability  of  the  nerve  is  altered 
during  the  passage  of  the  electric  current  (elec- 
trotonus);1  it  is  increased  in  the  neighborhood 
of  the  cathode  (catelectrotonus)  and  is  diminished 
in    the   neighborhood   of   the    anode   (anelectro- 

1  The  change  in  the  excitability  of  the  nerve  produced  by 
the  electric  current  is  so  generally  called  electrotonus  that  the 
term  cannot  well  be  changed.  It  should  not  be  confused  with 
the  electrotonus  described  on  page  000,  though  it  is  possible 
that  the  two  phenomena  have  a  similar  if  not  identical  first 
cause. 


120      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

tonus).  Ill  the  intrapolar  region,  the  cathodal 
touches  the  anodal  area  at  the  so-called  indifferent 
point.  This  point  approaches  the  cathode  when 
the  intensity  of  the  polarizing  current  is  increased. 

The  greater  the  length  of  nerve  between  the 
electrodes,  the  greater  the  extrapolar  electrotonus. 
Catelectrotonus  rises  rapidly  to  a  maximum  as 
soon  as  the  circuit  is  closed,  and  then  gradually 
wanes.  Anelectrotonus  develops  more  slowly  and 
does  not  reach  its  maximum  for  some  time  after 
closure. 

On  the  opening  of  the  circuit,  the  conditions  at 
the  anode  and  cathode  are  reversed,  the  irritability 
falls  at  the  cathode  and  rises  at  the  anode.  The 
fall  in  the  cathodal  region  is  of  short  duration 
and  the  irritability  soon  returns  again  towards 
normal.  In  the  anodal  region,  the  rise  on  open- 
ing is  unbroken. 

Changes  in  Conductivity.  —  We  have  seen 
that  the  irritability  is  altered  by  the  galvanic 
current.     The  conductivity  also  is  altered. 

Connect  a  dry  cell  through  a  pole-changer  with 
cross-wires  to  a  pair  of  non-polarizable  electrodes 
placed  in  the  holders  of  the  moist  chamber 
farthest  from  the  muscle  (Fig.  32).  Leave  one 
wire  uncoupled  until  the  current  is  wanted. 
Connect  another  cell  with  the  primary  coil  of 
the   inductorium    arranged    for   break  induction 


STIMULATION   OF   MUSCLE    AND   NERVE       121 


shocks,  placing  in  the  circuit  a  simple  key  and 
the  electro-magnetic  signal.  Lead  wires  from  the 
poles  of  the  secondary  coil  to  the  side  cups  of  a 
pole-changer  (without  cross-wires).  In  each  of 
the  remaining  two  holders  of  the  moist  chamber 
place  a  cork  pierced  by  two  metal  electrodes. 
One  wire  in  each  pair  should  be  insulated  from 
its  fellow  by  rubber 
tubing  drawn  over  the 
part  between  the  cork 
and  the  end  of  the  elec- 
trode to  be  applied 
to  the  nerve.  Connect 
the  wire  soldered  to 
the  basal  ends  of  these 
electrodes  with  the  re- 
maining cups  of  the 
pole-changer  in  the  sec- 
ondary circuit  of  the 
indue  torium 

smoked  drum  beneath  the  writing  point  of  the 
muscle  lever. 

Make  a  nerve-muscle  preparation.  Let  the 
nerve  rest  on  the  non-polarizable  electrodes  near 
the  cross-section.  Place  one  pair  of  the  metal 
electrodes  beneath  the  nerve  near  the  muscle,  the 
other  pair  near  the  non-polarizable  electrodes. 
The   clockwork    of    the    drum    should   be    fully 


Fig.  32. 


Arrange  the  signal  to  write  on  the 


122      GENERAL   PEOPERTIES    OF   LIVING   TISSUES 

wound  (not  over  wound),  and  the  drum  should 
revolve  at  its  most  rapid  speed.  Write  two 
muscle  curves.  For  the  first  stimulate  through 
the  metal  electrodes  nearer  the  muscle ;  for  the 
second  through  the  metal  electrodes  farther  from 
the  muscle. 

While  each  curve  is  writing,  let  a  tuning  fork 
record  its  vibrations  beneath  the  point  of  the 
the  muscle  lever.  To  mark  on  the  abscissa  of 
the  muscle  curve  the  exact  moment  at  which  the 
muscle  was  stimulated,  turn  back  the  drum  until 
the  writing  point  of  the  signal  lies  precisely  in 
the  line  described  by  it  when  the  current  was 
broken.  Now  stimulate  the  muscle  with  another 
induction  shock.  The  curved  ordinate  of  the 
muscle  lever  will  be  synchronous  with  the  ordi- 
nate of  the  signal. 

The  interval  between  the  moment  of  stimula- 
tion, as  recorded  by  the  signal,  and  the  beginning 
of  contraction,  is  greater  when  the  nerve  is  stim- 
ulated far  from  the  muscle.  The  difference  is 
the  time  required  for  the  nerve  impulse  to  tra- 
verse the  length  of  nerve  between  the  electrodes, 
provided  of  course  that  the  interval  between  the 
arrival  of  the  nerve  impulse  in  the  muscle  and 
the  beginning  of  the  contraction  is  the  same  in 
both  cases,  an  assumption  considered  reasonable 
by  most  physiologists. 


STIMULATION   OF   MUSCLE    AND    NERVE       123 

Write  now  three  other  pairs  of  curves :  one 
while  a  galvanic  current  passes  through  the  non- 
polarizable  electrodes  in  a  descending  direction 
(cathode  nearer  the  muscle);  a  second  while  an 
ascending  current  passes  (anode  nearer  the  mus- 
cle) ;  and  a  third,  after,  the  galvanic  current  has 
been  some  minutes  broken,  as  a  control.  During 
the  writing  of  these  curves  measure  the  velocity 
of  the  drum  with  the  tuning  fork  as  before. 

The  speed  of  the  nerve  impulse  will  be  found 
to  be  greater  than  normal  when  the  nerve  im- 
pulse starting  at  the  second  pair  of  metal  elec- 
trodes passes  through  an  extrapolar  cathodal 
area  (i.  e.  stimulation  during  descending  current), 
and  less  than  normal  when  that  region  is  made 
anodal  by  reversing  the  galvanic  current.  In 
other  words,  the  conductivity  of  the  nerve  has 
been  increased  by  cathodal  and  diminished  by 
anodal  stimulation. 

2.  Conductivity  is  diminished  by  strong  or  pro- 
tracted currents  in  the  cathodal  as  well  as  in  the 
anodal  region.  —  Place  two  non-polarizable  elec- 
trodes upon  the  nerve  about  3  cm.  apart.  Con- 
nect them  through  a  pole-changer  with  two  dry 
cells  (Fig.  33).  In  the  middle  of  the  intrapolar 
region  place  two  stimulating  electrodes  close 
together.  Connect  one  of  the  stimulating  elec- 
trodes directly  to  the  secondary  coil  of  an  indue- 


124      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

torium  arranged  for  single  induction  currents. 
Lead  from  the  other  stimulating  electrode  to  a 
piece  of  nerve  or  muscle  about  4  cm.  long,  and 
thence  to  the  secondary  coil.  The  introduction 
of  this  great  resistance  will  keep  most  of  the 
polarizing  current  in  the  short  bridge  of  nerve 
between  the  polarizing  electrodes.  Without  this 
resistance,   the    polarizing    current   would   pass 

through  the  stimulating 
A3    v2^  circuit  in  preference  to 

N  /Ct\/  crossing   the   nerve  be- 

/S7  tween    the    stimulating 

I      i  electrodes.   Observe  that 

the  nerve  impulse  cre- 
ated   by    the    stimulus 

Pig.  33>  cathodal   region,   if   the 

current  be  descending,  or 
the  anodal  region,  if  the  current  be  ascending,  in 
order  to  reach  the  muscle. 

Find  the  position  of  the  secondary  coil  at 
which  the  muscle  will  barely  contract  on  making 
the  stimulating  current.  Arrange  the  pole- 
changer  to  brin^  the  anode  between  the  stiinu- 
lating  electrodes  and  the  muscle,  and  make  the 
polarizing  current.  Stimulate  with  a  make  in- 
duction current  during  the  passage  of  the  polar- 
izing   current.     Open     the     polarizing     current. 


I 


~"u\  ^  y^2)    must  pass  through  the 


STIMULATION    OF   MUSCLE    AND   NERVE        125 

After  three  minutes'  rest,  bring  the  cathode  next 
the  muscle  and  make  the  polarizing  current  as 
before.  Then  stimulate  again  with  a  make  in- 
duction current   of  the  same  intensity  as  before. 

Contraction  will  be  absent,  or  at  most  very 
weak.  The  impulse  will  be  blocked  in  the 
cathodal  region.  In  truth,  during  the  passage  of 
strong  or  protracted  currents,  the  conductivity  is 
more  diminished  in  the  cathodal  than  in  the 
anodal  resrion. 

Griitzner  and  Tigerstedt  believe  that  the  open- 
ing contraction  is  due  to  the  stimulation  of  the 
nerve  or  muscle  by  the  polarization  current 
which  appears  when  the  galvanic  current  is 
broken.  The  polarization  current  may  be  said 
to  be  closed  when  the  galvanic  current  is  opened. 
These  observers,  therefore,  hold  that  stimulation 
takes  place  only  at  closure. 

We  are  now  in  a  position  to  account  for  the 
phenomena  described  by  the  law  of  contraction. 
The  irritability  of  the  nerve  is  increased  at  the 
cathode  on  closing,  and  at  the  anode  on  opening 
the  galvanic  current.  This  rise  of  irritability 
stimulates  the  nerve.  The  rise  at  the  cathode  is 
a  more  effective  stimulus  than  the  rise  at  the 
anode ;  consequently  with  weak  currents  the  first 
stimulus  to  produce  contraction  is  cathodal,  i.  e. 
at  the  closure  of  the  circuit.     As  the  current  in- 


126      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

tensity  is  increased,  the  anodal  rise  becomes  also 
effective,  and  contraction  is  secured  by  both  mak- 
ing and  breaking  the  current. 

But  we  have  to  deal  also  with  a  decrease  in 
irritability,   and,   still   more    important    for   the 
explanation  of  the  effects  of  strong  currents,  with 
a  decrease  in  conductivity.     The  irritability  and 
conductivity  are  decreased  on  closure  at  the  anode 
and  on  opening  at  the  cathode.     If  the  anode  is 
next  the  muscle  (Fig.  34),  the  decrease  in  con- 
ductivity on  closure  of  a  strong 
current  will  block  the  nerve  im- 
m^^)    ?""-?        pulse  coining  from  the  cathode  ; 
it  will  therefore  never  reach  the 

«c^3 |  —  *        muscle,   and    there    will   be   no 

Fig.  34.  contraction   on   closure.     If   the 

cathode  is  next  the  muscle,  the 
conductivity  may  be  so  decreased  on  opening  that 
the  nerve  impulse  coining  from  the  anode  may  be 
blocked.  The  decrease  at  cathode,  when  the  cur- 
rent is  broken,  is,  however,  less  marked  than  the 
decrease  at  anode  when  the  current  is  made,  so 
that  the  cathodal  decrease,  even  writh  strong 
currents,  sometimes  fails  to  block  the  impulse 
entirely.  In  that  case,  a  weak  contraction  may 
be  obtained  at  the  break  of  the  descending 
current. 


stimulation  of  muscle  and  nerve     127 

Stimulation  of  Human  Nerves 

Duchenne  devised  a  method  by  which  either  the 
motor  or  the  sensory  human  nerves  can  be  stimu- 
lated at  will,  and  the  reaction  of  single  muscles 
or  groups  of  muscles  to  electricity  determined. 
When  electrodes  are  placed  on  the  surface  of  the 
skin  and  the  circuit  is  made,  the  current  entering 
at  the  anode  will  spread  in  current  lines  through 
the  entire  body.  At  the  cathode,  all  these  lines 
will  converge  again.  The  density  of  the  current 
depends  on  the  concentration  of  the  current 
lines.  Thus  the  density  is  relatively  great  at 
the  electrodes,  and  becomes  rapidly  weaker  as 
the  lines  diverge  between  them.  The  smaller  the 
electrode,  the  greater  the  density.  The  stimulat- 
ing effect  depends  on  the  density.  With  small 
electrodes,  a  current  not  sufficient  to  cause  stimu- 
lation may  gradually  be  increased  in  strength 
until  the  density  at  the  electrode  becomes  great 
enough  to  stimulate,  while  in  all  other  regions  it 
is  not  yet  great  enough.  Thus  a  local  stimula- 
tion is  secured.  But  this  local  stimulus  does 
not  sufficiently  distinguish  between  the  sensory 
nerves  and  the  motor  nerves  and  muscles ;  for  in 
order  to  reach  the  deeper  lying  motor  nerves  and 
muscles,  the  current  must  pass  through  the  skin. 
The  resistance  of  the  epidermis  is  very  great,  and 


128       GENERAL    PROPERTIES    OF   LIVING   TISSUES 


currents  of  considerable  intensity  are  necessary 
to  overcome  it.  Once  through  the  epidermis,  the 
current  spreads  immediately  in  all  directions 
through  the  cutis,  where  it  stimulates  the  very 


Mm.  lumbricales 

* 


M.  opponens  digit,  min 

M.  flexor  digit,  min. 

M.  abd.  digit,  min. 

M.  palmaris  brevis 

N.    ulnaris   (ram.  vol. 
prof.) 

N.  medianus 

M.    flexor   digit,    subl. 
(ind.  and  minim.) 


M.  flexor,   digit. 
(II  &  III) 


subl 


M.  flexor  digit  profund. 

M.     ulnaris      internus 

(flexor  carp.  uln. ) 

M.  palm,  longus 

M.  pronator  teres 

N.  medianus 


N.  ulnaris 


M.  adductor  poll. 
M.  flexor  poll,  brevis 
M.  opponens  pollicis 
M.  abductor  poll,  brevis 


M.  flexor  pollicis  longus 


—  M.  flexor  digit,  subl. 


M.  rad.  internus  (flexor 
carp,  rad  ) 

M.  supin.  longus 


Fig  35.    The  motor  points  on  the  anterior  surface  of  the  forearm  and 
hand. 

numerous  sensory  nerves.  When  the  muscles  or 
motor  nerves  are  reached,  the  density  is  much 
reduced,  and  may  not  suffice  for  stimulation. 
Thus  the  result  may  be  not  motor  stimulation, 
but  simply  pain  from  stimulation  of  the  sensory 


STIMULATION    OF   MUSCLE    AND    NERVE       129 

nerves.  For  painless  motor  stimulation  it  is, 
therefore,  necessary  to  increase  the  strength  of 
the  current  which  reaches  the  muscle  or  motor 
nerve  and  to  diminish  the  density  of  the  current 


M.  inteross.  dors.  IV 
M.  abd.  digit,  min. 


M.  ext.  poll,  brevis 

M.  abd.  poll,  longus 

M.  ext.  indicis  propr. 
M.  ulnaris  extern. 

M.  rad.  ext.  brevis 


M.  ext.  pollicis  longus 
M.  ext.  indicis  propr. 

M.  ext.  dig.  min.  propr 
M.  ext.  dig.  communis 

M.  supin.  brevis 


M.  rad.  ext.  longus  - 
M.  supin.  longus  ■ 


Fig.  36.    The  motor  points  on  the  posterior  surface  of  the  forearm  and 
hand. 

at  the  electrodes.  These  ends  are  accomplished 
by  using  for  electrodes  large  metal  plates  cov- 
ered with  sponge  or  cotton  wet  with  saline  solu- 
tion. The  liquid  diminishes  greatly  the  resistance 
of  the  epidermis,  so  that  more  current  reaches 

9 


130      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

the  deeper  tissues ;  and  the  large  surface  offers  a 
broad  path  for  the  current,  so  that  the  current  lines 
are  not  so  concentrated  as  to  stimulate  painfully 
the  sensory  nerves  of  the  cutis.  One  sponge  elec- 
trode may  be  made  considerably  smaller  than  the 
other  without  forfeiting  this  advantage,  while  the 
smaller  size  makes  it  easier  to  localize  the  stimulus. 

Muscles  are  best  stimulated  through  their 
nerves,  for  two  reasons :  the  nerve  responds  to 
a  weaker  stimulus  than  the  muscle ;  and,  sec- 
ondly, it  is  much  easier  to  secure  contraction  of 
the  whole  muscle  by  stimulating  the  nerve  than 
by  attempting  to  pass  a  current  through  the 
muscle  directly.  The  smaller  electrode  should 
be  placed  over  the  nerve,  the  larger  on  some  in- 
different region.  The  indifferent  electrode  may 
be  placed  over  the  muscle  itself,  if  it  is  important 
that  the  resistance  shall  not  be  increased  by  the 
too  great  separation  of  the  electrodes. 

Duchenne  found  that  certain  points  were  es- 
pecially favorable  for  the  stimulation  of  indi- 
vidual muscles.  Remak  discovered  that  these 
"  motor  points  "  were  simply  the  places  at  which 
the  nerves  entered  the  muscle.  The  motor  points 
of  the  forearm  are  shown  in  Figs.  35  and  36. 

Stimulation  of  Motor  Points. — Arrange  the 
inductorium  for  single  induction  shocks.  .De- 
termine by  the  electrolytic  method  which  pole 


STIMULATION   OF    MUSCLE   AND    NERVE       131 

of  the  secondary  coil  is  the  cathode  when  the 
primary  current  is  broken  (page  158).  To  this 
pole  connect  the  small  (stimulating)  electrode ; 
to  the  other  pole  connect  the  large  (indifferent) 
electrode.  Place  the  indifferent  electrode  on 
the  arm  or  neck.  With  the  small  electrode 
make  out  the  motor  points  indicated  in  Figs.  35 
and  36. 

Polar  Stimulation  of  Human  Nerves.  —  In  the 
hands  of  the  earlier  observers  the  stimulation 
of  nerves  within  the  body  gave  results  often 
contrary  to  the  law  of  polar  stimulation  so  easily 
demonstrated  in  extirpated  nerves.  The  ex- 
planation of  these  inconstant  results  lay  in  the 
failure  to  comprehend  the  distinction  between 
the  stimulating  positive  and  negative  electrodes 
and  the  physiological  anode  and  cathode  (compare 
page  108).  Even  when  the  monopolar  method 
is  employed,  and  a  small  electrode  is  brought  as 
near  as  possible  to  the  nerve  to  be  stimulated, 
while  a  large  indifferent  electrode  is  placed  on 
some  other  part  of  the  body,  it  is  impossible  to 
secure  true  monopolar  stimulation.  The  current 
entering  at  the  anode  does  not  remain  in  the 
nerve,  but  very  soon  passes  out  into  the  sur- 
rounding tissues  (Fig.  37).  Hence  there  are 
physiological  cathodes  on  both  sides  of  the  posi- 
tive electrode,  and  for  the  like  reason  physiologi- 


132       GENERAL    PROPERTIES   OF   LIVING   TISSUES 


cal  anodes  on  both  sides  of  the  negative  electrode. 
Thus  both  anodal  and  cathodal  stimulation  take 
place,  whichever  electrode  rests  over  the  nerve. 
It  is  therefore  incorrect  to  speak  of  ascending 
and  descending  currents  in  the  case  of  nerves 
stimulated  in  situ.  It  should  be 
pointed  out,  too,  that  the  density 


^~jk 


cccccc 


AAAAAA 


Fig.  37. 


of  the  current  is  greater  on  the 
side  of  the  nerve  nearer  the 
electrode  than  on  the  more  deeply 

placed  side  cut  by  current  lines  already  rapidly 

diverging. 

With   these  facts   in   mind,  we  may  compare 

the  polar  stimulation  of  human  nerve  with  the 

law  already  determined  for  the  isolated  nerves 

of  the  frog  (page  115). 

The     Brass     Electrodes.  —  The    brass    electrodes, 
used    chiefly    for    the  stimulation  of   human  muscles 

and  nerves,  are  two  in  number: 
an  "indifferent"  electrode,  con- 
sisting of  a  brass  plate,  3x6 
cm.,  with  binding  post,  and 
a  "  stimulating  "  electrode,  of 
brass  rod,  G  cm.  long,  ringed 
at  one  end  and  provided  at  the 
other  with  a  binding  post.     Be- 


Fig.  38. 

tween  these  the  rod  is  insulated  with  rubber  tubing. 


The  electrodes  should  be  covered   with  cotton  wet 


STIMULATION    OF   MUSCLE   AND   NERVE       133 

with  normal  saline  solution.  The  larger  electrode 
may  be  fastened  upon  the  arm  or  other  indifferent 
region,  and  the  smaller  may  be  used  to  stimulate  the 
nerves  or  muscles,  for  example  the  abductor  indicis, 
or  to  find  the   "motor  points." 

Connect  8  dry  cells  in  series  (the  carbon  of 
one  cell  to  the  zinc  of  the  next,  etc.).  Coupling 
in  this  way  enables  the  electromotive  force  of 
each  cell  to  be  added  with  slight  loss  to  that  of 
the  others,  provided  the  resistance  in  the  circuit 
outside  the  cells  is  so  great  that  the  internal 
resistance  of  the  battery  disappears  in  compari- 
son, as  is  the  case  where  living  tissues  form  part 
of  the  circuit.  Connect  the  terminal  zinc  and 
carbon  pole  through  a  pole-changer  (with  cross- 
wires)  to  a  small  and  a  large  electrode  covered 
with  cotton  thoroughly  wet  with  strong  saline 
solution.  Place  the  small  electrode  over  the 
ulnar  nerve  between  the  internal  condyle  and 
the  olecranon,  a  little  above  the  furrow.  Make 
and  break  the  current.  If  no  contraction  is 
secured,  add  cells  to  the  battery  until  contraction 
occurs. 

It  will  be  found  that  the  first  contraction 
occurs  on  closure  with  the  cathode  over  the 
nerve.  With  this  strength  of  current  the  opening 
contraction  will  be  absent. 

Turn  the  pole-changer  so  as  to  bring  the  anode 


134      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

over  the  nerve,  and  increase  the  intensity  still 
further. 

A  strength  will  be  reached  at  which  closure 
with  the  anode  over  the  nerve  will  cause  contrac- 
tion, but  the  opening  of  the  current  will  still  be 
without  effect.  A  slightly  greater  intensity  will 
now  bring  out  the  anodal  opening  contraction.1 

In  the  mean  time  the  cathodal  closing  con- 
traction  has  increased  in  force  with  each  addition 
to  the  intensity  of  the  current.  With  about  18 
cells,  the  muscle  twitch  on  closure  may  give 
place  to  a  continued  contraction  or  tetanus,  the 
cathodal  closing  tetanus.  Further  increase  gives 
cathodal  opening  contraction,  and  finally  very 
strong  currents  sometimes  cause  anodal  closing 
tetanus.     Thus  we  have 

1.  Cathodal  closing  contraction. 

2.  Anodal  closing  contraction. 

3.  Anodal  opening  contraction. 

4.  Cathodal  closing  tetanus. 

5.  Cathodal  opening  contraction. 

6.  Anodal  closing  tetanus  (rare). 
Sometimes   the    anodal    opening   precedes  the 

anodal  closing  contraction. 

1  Sometimes  anodal  opening  contraction  precedes  the  closing 
contraction.  This  inconstancy  results  from  variations  in  cur- 
p  lit  strength  due  to  differences  in  the  tissues  surrounding  the 
nerve. 


STIMULATION   OF   MUSCLE   AND   NERVE       135 

The  apparent  deviation  from  the  law  of  polar 
excitation  (cathodal  on  closure,  anodal  on  open- 
ing) is  explained  by  the  presence  of  a  physi- 
ological anode  and  cathode  at  each  electrode, 
as  already  mentioned.  The  appearance  of  cath- 
odal closing  contraction  before  anodal  closing 
contraction  is  due  to  the  fact  that  when  the 
negative  electrode  lies  over  the  nerve  the  physi- 
ological cathode  will  be  found  on  the  side  of  the 
nerve  next  the  electrode.  The  nearer  the  elec- 
trode, the  greater  the  current  density,  and  hence 
the  earlier  the  threshold  value  is  reached.  When, 
however,  the  positive  electrode  lies  over  the 
nerve,  the  physiological  cathode  will  be  found 
on  the  side  of  the  nerve  farther  from  the  elec- 
trode, where  the  density  is  less,  owing  to  the 
divergence  of  the  current  lines.  The  threshold 
value  will  be  reached  first  at  the  point  of  higher 
density,  and  consequently  the  first  contraction 
will  appear  while  the  negative  electrode  rests 
over  the  nerve.  The  anodal  opening  contraction 
appears  before  the  cathodal  opening  contraction 
for  a  similar  reason. 

Reaction  of  Degeneration.  —  Whenever  a  nerve 
is  severed,  the  portion  separated  from  the  cell  of 
origin  of  the  nerve  "  degenerates."  The  degener- 
ation does  not  begin  at  the  section  and  advance 
to    the   terminal   branches,   but    takes  place    al- 


136      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

most  or  quite  simultaneously  throughout  the 
nerve.  Eanvier  states  that  it  begins  first  in  the 
end  plates.  Severed  nerves  in  the  brain  and 
spinal  cord  degenerate  in  the  same  way,  and  this 
"Wallerian  degeneration"  (Waller,  1850)  is  a 
valuable  aid  in  tracing  the  path  of  nerve  fibres 
in  the  central  nervous  system.  Degeneration  is 
accompanied  by  changes  in  the  reaction  to  the 
electric  current  which  form  a  valuable  aid  in  the 
diagnosis  of  the  seat  of  the  lesion  in  cases  of 
paralysis.  The  muscle  reacts  imperfectly,  or  not 
at  all,  to  the  brief  induction  current,  while  its 
reaction  to  the  long  galvanic  current  may  even 
be  greater  than  usual. 

Expose  each  gastrocnemius  muscle  in  a  frog, 
the  left  sciatic  nerve  of  which  has  been  severed 
ten  days  before  this  experiment.  Stimulate  each 
muscle  with  weak  induction  currents  and  with 
the  galvanic  current. 

The  muscle,  the  nerves  of  which  are  degen- 
erated, reacts  more  readily  to  the  galvanic  current 
than  to  the  brief  induction  current.  The  normal 
muscle  shows  the  opposite  reaction. 

In  man,  the  reaction  of  degeneration  in  the 
case  of  muscle  consists  of  a  lessened  or  lost 
excitability  to  the  induced  current  with  increased 
excitability  to  the  galvanic  current.  The  duration 
of  contraction  may  be  greater  than  normal.     In 


STIMULATION   OF   MUSCLE   AND    NERVE       137 

polar  stimulation,  anodal  closing  contraction  may 
appear  before  cathodal  closing  contraction,  —  a 
reversal  of  the  normal  sequence. 

In  degenerated  nerve  there  is  of  course  a  total 
loss  of  irritability,  corresponding  to  the  destruc- 
tion of  the  axis-cylinder. 

Galvanotropism 

Paramecium.  —  Connect  two  non-polarizable 
electrodes  through  a  pole-changer  with  a  dry  cell. 
On  a  glass  microscope-slide  make  with  wax  an 
enclosure  about  one  centimetre  square  and  a  few 
millimetres  high.  Place  in  this  a  little  hay 
infusion  containing  Paramecia.  Bring  near  the 
two  opposite  sides  of  the  wax  cell  non-polarizable 
electrodes,  provided  with  a  thick  thread  that  shall 
dip  into  the  infusion.  Examine  the  infusion  with 
a  very  low  power.     Close  the  key. 

Upon  closure  each  Paramecium  turns  the  an- 
terior end  of  the  body  towards  the  cathode  and 
swims  in  that  direction.  In  a  very  short  time 
the  anodal  region  is  free,  and  the  Paramecia  are 
gathered  at  the  cathode,  where  they  remain  so 
long  as  the  current  flows. 

Change  the  direction  of  the  current. 

The  Paramecia  now  turn  to  the  anode  and 
swim  in  that  direction,  but  the  anodal  grouping 
is  less  complete  than  the  cathodal,  and  lasts  but 


138      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

a  short  time.  Careful  observation  shows  that 
in  Paramecium  the  galvanic  reaction  consists  in 
placing  the  long  axis  of  the  bod)7  in  the  current 
lines.  The  outermost  individuals  in  the  liquid 
will  therefore  describe  a  curve  corresponding  to 
the  curved  outer  current  lines. 

All  protozoa  and  many  other  animals  (for  ex- 
ample, the  tadpole  and  the  crayfish)  show  gal- 
vanotropism,  but  in  some,  movement  on  closure 
is  toward  the  positive  pole  (positive  galvano- 
tropism). 

These  experiments  on  skeletal,  smooth,  and 
cardiac  muscle,  on  nerve,  and  on  infusoria,  sug- 
gest that  polar  excitation  occurs  wherever  a  gal- 
vanic current  passes  through  irritable  tissue. 
Further  experience  would  confirm  this  view.  We 
have  seen  that  the  changes  at  the  cathode  when 
the  current  is  made  are  not  momentary,  as  re- 
quired by  the  hypothesis  of  DuBois-Eeymond, 
but  continue  so  long  as  the  current  flows.  This 
fact  appears  still  more  clearly  when  the  influence 
of  the  duration  of  the  current  is  examined. 

Influence  of  Duration  of  Stimulus 

1.  Smoke  a  drum.  Arrange  a  muscle  lever  to 
write  on  the  smoked  paper.  Prepare  non-polariz- 
able  electrodes  and  fasten  them  on  the  glass  plate 


STIMULATION   OF   MUSCLE   AND   NERVE       139 

of  the  nerve  holder.  Arrange  the  inductoriuni 
for  maximal  induction  currents.  Lead  from  the 
secondary  coil  to  a  pair  of  the  end  cups  of  the 
pole-changer  (without  cross-wires),  as  in  Fig.  39. 
To  the  opposite  cups  of  the  pole-changer  bring 
wires  from  a  dry  cell. 
Connect  the  remaining 
cups  with  the  non-polar- 
izable  electrodes.  Turn 
the  rocker  towards  the  in- 
duction coil.  Fasten  the 
pelvic  attachment  of   the  Kg.  39. 

curarized    sartorius    in 

the  muscle  clamp.  Tie  a  thread  to  the  fragment 
of  tibia,  and  fasten  the  thread  to  the  upright  pin 
of  the  muscle  lever,  so  that  the  horizontal  muscle 
shall  record  its  contraction  on  the  drum.  Start 
the  drum  at  moderate  speed.  Record  contrac- 
tions, (1)  with  maximal  break  shocks,  (2)  with 
closure  of  galvanic  current.    Compare  the  curves. 

The  curve  from  galvanic  stimulation  will  be  of 
greater  height  and  duration,  and  the  summit  of 
the  curve  will  be  less  pointed,  indicating  that 
the  muscle  remains  longer  in  the  stage  of  ex- 
treme shortening. 

Other  evidence  that  the  duration  of  the  stimu- 
lus modifies  the  character  of  the  contraction  is 
afforded  by  the  following  experiments :  — 


140      GENERAL    PROPERTIES   OF    LIVING   TISSUES 

2.  Make  two  cuts,  5  mm.  apart,  through  the 
frog's  stomach  at  right  angles  to  the  long  axis. 
Hang  the  ring  thus  secured  in  the  moist  cham- 
ber. Pass  a  bent  hook  through  the  lower  end  of 
the  ring,  and  attach  it  by  means  of  a  fine  copper 
wire  to  the  hook  on  the  muscle  lever.  Carry  the 
end  of  the  copper  wire  to  the  binding  post  on  the 
muscle  lever. 

Stimulate  not  more  than  twice  with  single  in- 
duction currents  of  a  strength  about  the  threshold 
value  for  skeletal  muscle  of  frog. 

There  will  be  no  contraction. 

Stimulate  with  galvanic  current  (two  dry  cells),1 
writing  three  curves,  the  duration  of  closure  be- 
ing approximately  one-fifth  second,  one,  and  five 
seconds,  respectively.     Compare  the  curves. 

The  maximum  shortening  with  currents  of 
brief  duration  (^  second)  is  very  much  less  than 
with  currents  of  three  or  four  seconds  or  over. 
The  briefer  the  current  also,  the  quicker  will  the 
maximum  shortening  be  reached,  and  the  quicker 
will  be  the  relaxation. 

3.  If  the  galvanic  current  is  very  rapidly  made 
and  broken,  the  muscle  will  not  contract. 

1  If  the  muscle  does  not  respond,  wrap  it  with  filter  paper 
moistened  with  normal  saline  solution,  and  wait  until  the  tonic 
contraction  due  to  the  cutting  has  passed  off.  The  tonus  may 
sometimes  be  lessened  by  passing  a  galvanic  current  through  the 
preparation  (p.  153). 


STIMULATION   OF   MUSCLE   AND    NERVE       141 

The  same  is  true  of  the  ureter  (Engelmann). 

4.  Tonic  Contraction.  —  Examine  the  contrac- 
tion curve  already  recorded  by  the  smooth 
muscle  of  the  frog's  stomach.  Note  that  the 
muscle  remains  contracted  during  the  passage 
of  the  current.  The  curves  secured  from  the 
curarized  sartorius  (page  139)  also  show  this, 
but  to  a  much  less  degree ;  the  sartorius  does 
not  resume  its  former  length  after  the  twitch  or 
closure  of  the  galvanic  current,  but  remains  con- 
tracted to  a  slight  extent.  This  tonic  contrac- 
tion appears  much  more  plainly  in  fatigued 
muscles. 

Fatigue  a  sartorius  muscle  by  stimulating  it 
with  a  galvanic  current  repeatedly  made  and 
broken.  After  a  time,  the  twitch  on  closure  will 
become  very  feeble,  and  finally  will  disappear, 
while  the  tonic  shortening  during  the  passage  of 
the  current  is  still  very  evident. 

5.  The  influence  of  duration  is  shown  also  in 
the  opening  contraction. 

Fasten  the  pelvic  attachment  of  a  sartorius 
muscle  in  the  muscle  clamp  and  connect  the 
other  end  with  the  upright  pin  of  the  muscle 
lever,  so  that  the  horizontal  muscle  shall  record 
its  contraction  on  a  drum.  Place  the  non-polar- 
izable  electrodes  on  the  ends  of  the  muscle. 
Allow  the  "galvanic  current  from  a  dry  cell  to 


142      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

pass  through  the  muscle  until  the  closure  tonic 
contraction  has  disappeared,  then  open  the  key. 
Neglect  the  opening  twitch. 

The  muscle  will  not  return  to  its  original 
length,  but  will  remain  contracted  for  a  time 
(opening  tonic  contraction). 

Close  the  key  again. 

The  tonic  contraction  will  disappear. 

The  galvanic  current  in  this  case  checks  (in- 
hibits) a  contraction.  This  new  action  is  dis- 
cussed on  page  153. 

6.  Rhythmic  Contraction.  — That  the  galvanic 
current  acts  as  a  stimulus  so  long  as  it  continues 
to  flow  is  shown  also  by  the  fact  that  its  passage 
through  contractile  tissue  may  cause  the  muscle 
to  fall  into  rhythmic  contractions.  These  are 
easy  to  produce  in  muscles  which  normally  con- 
tract in  rhythms,  for  example,  the  heart ;  but 
they  may  under  some  circumstances  be  observed 
also  in  smooth  muscle,  and  even  in  skeletal 
muscles. 

Connect  a  dry  cell  through  a  simple  key  with 
the  metre  posts  of  the  rheochord.  Join  the  non- 
polarizable  electrodes  to  the  positive  post  and  the 
slider.  Bring  the  slider  against  the  positive  post, 
so  that  no  current  shall  flow  through  the  elec- 
trodes when  they  are  joined  by  the  tissue. 

Expose  the  heart.     With  a  sharp  knife  bisect 


STIMULATION    OF   MUSCLE   AND   NERVE       143 

the  ventricle  transversely.  Best  this  "apex" 
preparation  between  the  tips  of  two  non-polar- 
izable  boot  electrodes.  Keep  the  tissue  moistened 
with  normal  saline  solution,  but  avoid  excess. 
Close  the  key.     Move  the  slider  along  the  wire. 

When  the  current  taken  off  reaches  the  thresh- 
old value,  the  apex  will  begin  to  beat  rhyth- 
mically. Increasing  the  current  strength  will 
increase  (within  limits)  the  frequency  of  con- 
traction. 

Skeletal  Muscle.  —  The  curarized  sartorius  may 
sometimes  be  brought  into  rhythmic  contraction 
by  constant  currents  (Hering).  If  the  irrita- 
bility of  the  muscle  at  the  point  of  stimulation 
be  increased  by  applying  to  the  cathodal  region 
a  two  per  cent  solution  of  sodium  carbonate,  the 
constant  current  will  produce  strong  rhythmic 
contractions. 

Smoke  a  drum.  Fasten  the  pelvic  end  of  the 
sartorius  in  the  muscle  clamp,  and  attach  the 
tibial  end  by  a  thread  to  the  vertical  pin  on 
the  muscle  lever  so  that  the  horizontally  extended 
muscle  may  write  its  contraction  on  a  drum. 
Lay  on  the  tibial  fifth  of  the  muscle  a  piece  of 
filter  paper,  wet  with  two  per  cent  solution  of 
sodium  carbonate.  Connect  a  dry  cell  through 
a  simple  key  with  the  metre  posts  of  the  rheo- 
chord.      Connect  the   non-polarizable  electrodes 


144      GENERAL    PROPERTIES   OF   LIVING   TISSUES 

with  the  positive  post  and  the  slider.  Bring  the 
slider  near  the  positive  post.  When  the  sodium 
carbonate  has  acted  for  15  minutes,  bring  the 
cathode  against  the  tibial  end,  the  anode  against 
the  pelvic  end  of  the  muscle.  Close  and  open  the 
circuit,  moving  the  slider  meanwhile  to  find 
the  current  which  will  give  closing  contraction. 
At  this  point  keep  the  circuit  closed. 

Rhythmical  contractions  usually  appear. 

Periodic  contractions  are  observed  also  in 
smooth  muscle,  stimulated  with  the  constant 
current.  Any  form  of  constant  stimulus  will 
serve  to  produce  them,  pressure  —  as  in  the 
heart,  bladder,  and  intestine  —  and  chemical 
action,  being  especially  noteworthy. 

Continuous  Galvanic  Stimulation  of  Nerve  may 
cause  the  Periodic  Discharge  of  Nerve  Impulses.  — 
If  two  non-polarizable  electrodes  are  allowed  to 
rest  on  the  muscle  (horizontally  suspended),  and 
are  connected  to  a  capillary  electrometer,  the 
meniscus  of  which  is  projected  through  a  slit 
onto  rapidly  moving  sensitized  paper,  the  shadow 
of  the  meniscus  will  make  a  straight  line  on  the 
photographic  paper  so  long  as  the  muscle  is  at 
rest.  When,  however,  the  nerve  of  the  muscle 
is  stimulated  with  the  galvanic  current  and 
closing  tetanus  appears,  the  straight  line  will  be 
broken  by  10-15  oscillations  per  second.     These 


STIMULATION    OF   MUSCLE    AND   NERVE      145 

oscillations  are  produced  by  the  difference  of 
potential  created  by  each  contraction  wave  as  it 
passes  over  the  muscle  (contracting  muscle  is 
negative  towards  muscle  at  rest,  see  page  302), 
and  demonstrate  that  the  tetanus  is  a  fusion 
of  individual  contractions  produced  by  successive 
stimuli. 

Hence,  nerve,  like  muscle,  responds  to  a  contin- 
uous stimulus  by  a  periodic  discharge  of  energy. 

Ulnar  Nerve.  —  Connect  15  dry  cells  in  series 
(zinc  to  carbon),  and  join  the  last  zinc  and  carbon 
through  a  key  to  a  small  brass  stimulating 
electrode  one  cm.  in  diameter,  and  a  large  "  in- 
different" electrode  (brass  plate  6.5  x  3.5  cm. 
covered  with  cotton  wTet  in  solution  of  common 
salt).  Hold  the  indifferent  electrode  in  the  left 
hand,  and  apply  the  stimulating  electrode  to  the 
ulnar  nerve  at  the  elbow. 

A  peculiar  tingling  sensation  will  be  felt  so 
long  as  the  current  flows. 

Polarization  Current.  —  Let  the  sciatic  nerve 
rest  on  a  pair  of  non-polarizable  electrodes  in 
the  moist  chamber.  Connect  the  electrodes  to 
the  side  cups  of  the  pole-changer  (without  cross- 
wires).  Connect  one  end  pair  of  the  pole-changer 
cups  with  a  dry  cell.  Turn  the  rocker  to  the 
opposite  side  to  prevent  the  battery  current  from 
reaching  the  electrodes  until  it  is  wanted.     Con- 

10 


146      GENERAL   PROPERTIES   OF   LIVING  TISSUES 

nect  the  remaining  pair  of  cups  through  a  closed 
short-circuiting  key  with  the  capillary  electrom- 
eter. Let  the  galvanic  current  flow  some  min- 
utes through  the  nerve,  then  turn  the  rocker 
towards  the  electrometer  and  open  the  short- 
circuiting  key. 

Note  a  movement  of  the  meniscus  in  a  direction 
indicating  that  the  former  cathode  is  now  posi- 
tive to  the  former  anode. 
^^         _        /^~-\   J    The  nerve  is  polarized. 

(2/-  - JLJJ \ y\        [f|        Positive  Variation. — 

\     /  "x — '    If  the  polarizing  current 

1   1  is  strong  and  brief,  the 

negative  polarization 
after-current  will  speed- 
ily give  place  to  a  positive  current,  i.  e.  one  in  the 
direction  of  the  polarizing  current.  This  positive 
current  is  really  an  action  current.  When  the 
polarizing  current  is  broken,  the  rise  of  irritabil- 
ity at  the  anode  stimulates  points  nearer  the 
anode  more  strongly  than  points  farther  away. 
Points  nearer  the  anode  become,  therefore,  nega- 
tive to  points  farther  away,  and  a  current  flows 
through  the  electrometer  circuit  from  the  less 
negative  to  the  more  negative  pole,  and  through 
the  nerve  in  the  direction  from  anode  to  cath- 
ode. This  positive  variation  is  seen  only  in 
living  nerves. 


Fig.  40. 


STIMULATION   OF  MUSCLE   AND    NERVE       147 

Polar  Fatigue.  —  Connect  non-polarizable  elec- 
trodes through  a  simple  key  with  a  dry  cell. 
Fatigue  a  sartorious  muscle  by  opening  and  clos- 
ing the  galvanic  circuit  (leave  a  brief  interval 
between  opening  and  closure).  Closure  will  at 
length  be  followed  by  no  contraction.  Arrange 
an  inductorium  for  single  induction  currents  (the 
pole-changer  may  be  placed  in  the  primary  cir- 
cuit as  a  simple  key).  Test  now  the  irritability 
of  the  muscle  by  stimulating  it  with  single  induc- 
tion currents. 

The  muscle  will  be  irritable  except  in  the  cath- 
odal region.     The  fatigue  has  been  local  (polar). 

Opening  and  Closing  Tetanus.  —  1.  Arrange  a 
moist  chamber  with  a  muscle  lever  to  write  on  a 
smoked  drum.  Place  two  non-polarizable  elec- 
trodes in  the  moist  chamber  and  connect  them 
through  a  pole- changer  with  a  dry  cell.  Make  a 
nerve  muscle  preparation  from  a  frog  that  has 
just  been  brought  from  a  cold  room  into  the  warm 
laboratory.  Secure  the  femur  in  the  femur  clamp 
of  the  moist  chamber.  Let  the  nerve  rest  on  the 
non-polarizable  electrodes.  Attach  the  muscle 
to  the  lever.  Bring  the  writing  point  against  the 
slowly  moving  drum.     Close  the  key. 

If  the  frog  has  been  well  cooled  (below  10°  C), 
the  muscle  will  fall  into  tetanus  both  on  closing 
and  on  opening  the  circuit.     Note  that  the  curve 


148      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

is  quite  regular.  If  tetanus  fails  to  appear,  paint 
the  cathodal  region  with  one  per  cent  solution  of 
sodic  carbonate,  thus  raising  the  irritability,  and 
repeat  the  experiment.  The  curve  secured  in 
this  way  is  likely  to  be  irregular. 

Produce  opening  tetanus,  and  while  the  muscle 
is  contracting  close  the  current  again. 

The  tetanus  will  disappear ;  the  irritability 
will  be  reduced  in  the  anodal  region,  from  the 
polarization  of  which  the  tetanus  was  produced. 

Open  the  current  again.  When  the  tetanus 
reappears  reverse  the  pole-changer  and  close  the 
current. 

The  tetanus  will  be  increased ;  the  irritability 
in  the  former  anodal  region  will  suffer  a  catelec- 
trotonic  increase. 

2.  A  beautiful  demonstration  of  polar  excitation 
may  be  made  in  this  experiment.  Connect  the 
electrodes  in  such  a  way  that  the  intrapolar  cur- 
rent shall  be  descending  (i.e.  towards  the  muscle). 
When  the  opening  tetanus  appears,  cut  away 
the  anode  by  severing  the  nerve  between  the 
electrodes. 

The  contraction  ceases  witli  the  removal  of  the 
source  of  stimulation. 

3.  The  stimulating  effect  of  the  salts  of  the 
alkalies  has  been  explained  by  their  attraction 
for  water,  the  loss  of  which  increases  the  effect 


STIMULATION   OF   MUSCLE   AND    NERVE       149 

of  the  galvanic  current  on  nerve.  When  the 
irritability  of  the  nerve  is  raised  by  drying,  weak 
currents  may  give  opening  contractions,  although 
they  are  absent  in  normal,  uninjured  nerves. 
The  interval  between  the  opening  of  the  current 
and  the  resulting  contraction  is  then  markedly 
long.  In  nerves  in  the  first  stage  of  drying  the 
intensity  of  the  nerve  impulse  (height  of  con- 
traction of  attached  muscle)  is  also  more  than 
usually  dependent  on  the  duration  of  the 
current. 

4.  The  opening  tetanus  (so-called  Eitter's  tet- 
anus) is  probably  caused  by  the  rise  of  irritabil- 
ity, which  takes  place  in  the  anodal  region  when 
the  current  is  shut  off,  acting  on  a  nerve  already 
in  latent  excitation.  A  similar  condition  can  be 
produced  as  follows  :  — 

Smoke  a  drum.  Connect  a  dry  cell  through  an 
open  key  and  an  electro-magnetic  signal  with  the 
metre  posts  of  the  rheochord  (Fig.  41).  Connect 
the  zero  post  and  the  slider  of  the  rheochord  with 
the  pole-changer  (with  cross-wires),  and  the  latter 
with  two  non-polarizable  electrodes  placed  in  the 
moist  chamber.  Make  a  nerve-muscle  prepara- 
tion, and  secure  the  femur  in  the  femur  clamp 
of  the  moist  chamber.  Attach  the  muscle  to  the 
muscle  lever.  Bring  the  writing  points  of  the 
muscle   lever   and    the  electro-magnetic    signal 


150      GENERAL   PROPERTIES   OF   LIVING   TISSUES 

against  the  smoked  surface  in  the  same  vertical 
line.  Let  the  nerve  rest  on  the  non-polarizable 
electrodes.  In  the  remaining  two  posts  in  the 
moist  chamber  fasten  stimulating  electrodes. 
Connect  the  latter  to  the  inductorium,  arranged 
for  tetanizing  currents,  short-circuiting  key  closed. 
Bring  the  stimulating  electrodes  against  the  nerve 
between  the   non-polarizable  electrodes  and   the 


Fig.  41. 


muscle.  Let  the  secondary  coil  be  at  such  a  dis- 
tance that  the  tetanizing  current  will  be  just 
below  the  threshold  value.  Turn  the  pole-changer 
so  that  the  anode  shall  be  next  the  tetanizing 
electrodes.  Make  and  break  the  galvanic  current, 
recording  the  contraction  on  a  slowly  moving 
drum.  Now  open  the  short-circuiting  key,  and 
after  half  a  minute,  and  while  the  sub-minimal 
tetanizing  current  is   still    passing    through   the 


STIMULATION    OF   MUSCLE    AND   NERVE       151 

nerve,  make  and  break  the  galvanic  current 
again. 

A  moderately  strong  galvanic  current  will  now 
produce  an  opening  tetanus  (anodal  stimulation 
of  a  region  the  irritability  of  which  has  been 
raised  by  the  sub-minimal  tetanizing  current). 
Other  effects  are  a  lengthening  of  the  latent 
period,  and  an  increased  dependence  on  the 
duration  of  the  galvanic  current  (see  page  138). 

Ee verse  the  pole-changer,  so  that  the  tetanizing 
electrodes  fall  in  the  cathodal  region.  Eepeat 
the  experiment,  comparing  the  results  of  cathodal 
stimulation  without  and  with  the  sub-minimal 
tetanizing  current. 

With  sub- minimal  tetanization,  an  increase  in 
the  height  of  the  closing  contraction,  when  the 
galvanic  current  is  not  too  strong,  will  be  seen  ; 
when  the  galvanic  current  is  stronger,  closing 
tetanus  will  also  be  observed. 

Polar  Excitation  in  Injured  Muscle.  —  Smoke  a 
drum.  Make  non-polarizable  electrodes.  Con- 
nect a  dry  cell  through  a  simple  key  and 
pole-changer  (with  cross-wires)  with  the  non- 
polarizable  electrodes.  Prepare  a  sartorius  mus- 
cle with  bony  attachments.  Fasten  the  pelvic  end 
in  the  muscle  clamp.  Tie  a  thread  to  the  tibial 
end,  and  fasten  the  thread  to  the  upright  pin  of 
the  muscle  lever,  so  that  the  muscle  is  extended 


152      GENERAL   PROPERTIES   OF  LIVING  TISSUES 

horizontally.  Bring  the  writing  point  against  the 
drum.  Light  a  Bun  sen  burner.  Heat  a  wire, 
and  kill  the  pelvic  end  of  the  muscle  by  laying 
the  hot  wire  against  it.  Bring  one  non-polar- 
izable  electrode  upon  each  end  of  the  muscle. 
Arrange  the  pole-changer  so  that  the  cathode 
shall  be  at  the  pelvic  end,  and  the  current  there- 
fore "  atterminal,"  i.  e.  directed  toward  the 
"thermal  cross-section."     Close  the  simple  key. 

No  contraction,  or  a  very  slight  contraction, 
will  be  seen. 

Open  the  key.  Eeverse  the  pole-changer,  so 
that  the  current  shall  be  "  abterminal."  Close 
the  simple  key. 

The  ordinary  closing  contraction  will  be  seen. 

The  great  difference  here  shown  between  the 
polar  excitability  in  the  uninjured  and  injured 
region  is  probably  due  to  chemical  changes  in 
the  injured  part.  Similar  results  can  be  obtained 
by  painting  the  end  of  the  muscle  with  one  per 
cent  solution  of  acid  potassium  phosphate.  The 
irritability  is  lessened  by  this  salt,  but  returns  to 
normal  if  the  altered  end  of  the  muscle  is  bathed 
in  0.6  per  cent  sodium  chloride  solution. 

Sodium  carbonate  has  an  effect  opposite  to  that 
of  the  potassium  salts. 

Wet  the  pelvic  end  of  a  fresh  muscle  with  one 
per  cent   solution   of  sodic  carbonate.     After   a 


STIMULATION    OF   MUSCLE   AND    NERVE        153 

short  time,  test  the  irritability  to  weak,  ascend- 
ing (i.  e.  cathode  at  pelvic  end)  currents. 

The  closure  of  ascending  currents  will  give 
extraordinarily  large  contractions. 

The  cause  of  this  change  in  irritability  is  not 
the  presence  of  dead  contractile  tissue,  for  elec- 
trodes can  be  wrapped  in  dead  muscle  and  used 
to  stimulate  normal  muscle  without  loss  of  irri- 
tability being  noticeable. 

When  the  end  of  the  fibre  is  killed,  the  patho- 
logical change  passes  gradually  through  the 
whole  of  the  fibre. 


Polar  Inhibition  by  the  Galvanic  Current 

It  remains  now  to  consider  the  inhibitory 
action  of  the  galvanic  current,  to  which  attention 
was  called  on  page  142. 

Heart.  —  Connect  a  dry  cell  through  a  simple 
key  with  the  0  and  1  metre  posts  of  the  rheochord. 
Connect  non-polarizable  electrodes  through  a  pole- 
changer  with  cross-wires  (Fig.  30),  with  the  slider 
and  the  positive  post  of  the  rheochord.  Pith  the 
brain,  not  the  cord,  of  a  frog,  and  place  the  animal, 
back  down,  in  the  holder  (Fig.  29,  page  112),  and 
expose  the  heart,  without  unnecessary  loss  of 
blood,  according  to  the  method  described  on  page 
112.     Open  the  delicate  membrane  (pericardium) 


154      GENERAL   PROPERTIES   OF   LIVING  TISSUES 

which  surrounds  the  heart.  Let  one  electrode 
rest  on  the  larynx.  Lay  upon  the  tip  of  the 
other  electrode  a  strand  of  lamp  wick  or  absor- 
bent cotton  wet  with  normal  saline  solution. 
Bring  this  electrode  over  the  heart  so  that  the 
free  end  of  the  strand  rests  on  the  ventricle  and 
moves  with  it.  Turn  the  pole-changer  to  make 
this  electrode  the  anode.     Make  the  current. 

At  each  systole,  the  portion  of  the  ventricle 
immediately  about  the  anode  will  not  contract 
with  the  rest,  but  will  remain  relaxed  (local  dias- 
tole). Thus  while  the  greater  part  of  the  ven- 
tricle becomes  pale  as  the  blood  is  squeezed  out 
of  its  wall  by  the  contraction,  the  anodal  region 
remains  dark  red.  From  this  region  the  relaxa- 
tion spreads  over  the  rest  of  the  ventricle.  Re- 
verse the  pole-changer.     Break  the  current. 

The  cardiac  electrode  is  now  the  cathode.  In 
the  systole  following  the  breaking  of  the  current, 
the  cathodal  region  will  remain  relaxed  during 
contraction  of  the  ventricle. 

This  experiment  demonstrates  that  the  galvanic 
current  not  only  may  stimulate,  but  may  check 
or  inhibit  contraction.  In  the  former  case,  the 
conversion  of  potential  into  active  energy  is  set 
going;  in  the  latter,  it  is  prevented.  Inhibi- 
tion plays  a  large  part  in  the  physiology  of  the 
day. 


STIMULATION  OF  MUSCLE  AND  NERVE   155 

Polar    Inhibition   in    Veratrinized   Muscle.  —  A 

similar  inhibitory  effect  can  be  demonstrated  in 
skeletal  muscle  previously  placed  in  continued 
("tonic")  contraction  by  veratrine  poisoning. 
Inject  with  a  fine  glass  pipette  seven  drops  of 
one  per  cent  solution  of  veratrine  acetate  in  the 
dorsal  lymph  sac  of  a  frog. 

Arrange  two  muscle  levers  to  write  on  a  drum. 
Between  them  place  an  electromagnetic  signal. 
Let  all  three  writing  points  be  in  the  same  vertical 
line.  Connect  a  dry  cell  through  a  simple  key 
with  an  inductorium  arranged  for  single  induc- 
tion shocks.  Connect  non-polarizable  electrodes 
through  another  simple  key  and  the  electro- 
magnetic signal  with  a  dry  cell.  Prepare  a 
sartorius  muscle  with  pelvic  and  tibial  attach- 
ments. Fasten  the  muscle  about  the  middle  in 
the  cork  clamp.  Fasten  the  cork  clamp  verti- 
cally in  the  jaws  of  the  muscle  clamp.  Carry 
threads  from  each  end  of  the  muscle  to  one  of 
the  muscle  levers.  Place  the  non-polarizable 
electrodes  near  the  respective  ends  of  the  mus- 
cle. Note  which  is  the  anode.  Bring  wires 
from  the  secondary  coil  of  the  inductorium  to 
the  ends  of  the  muscle.  Start  the  drum  mov- 
ing slowly.  Stimulate  the  muscle  with  a  single 
induction  shock.  There  will  be  a  prolonged  con- 
traction, characteristic  of  veratrine  poisoning.    So 


156      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

soon  as  this  contraction  is  well  under  way,  make 
the  constant  current. 

The  anodal  half  of  the  muscle  will  show  a  dis- 
tinct relaxation  ;  the  cathodal  half  will  not  relax, 
but  may  even  contract  a  little  more. 

Stimulation  affected  by  the  Form  of  the 
Muscle 

Connect  a  dry  cell  through  a  simple  key  to 
the  metre  posts  of  the  rheochord.  Bring  wires 
from  the  non-polarizable  electrodes  to  the  positive 
post  and  the  slider,  interposing  the  pole-changer 
with  cross-wires  so  that  the  direction  of  the  cur- 
rent can  be  changed.  Place  the  slider  against 
the  positive  post,  so  that  all  the  current  passes 
back  to  the  cell. 

Prepare  a  curarized  sartorius  muscle  with  its 
bony  attachments.  Fasten  the  pelvic  fragment 
in  the  muscle  clamp.  Tie  a  thread  about  the 
tibia  and  fasten  the  thread  to  the  upright  pin  of 
the  muscle  lever.  Let  the  cathode  rest  on  the 
tibial  end  of  the  muscle,  the  anode  on  the  pelvic 
end  ;  the  current  will  then  be  descending.  Move 
the  slider  a  few  centimetres  away  from  the  posi- 
tive post,  and  make  the  current.  If  no  contrac- 
tion follows,  move  the  slider  farther  along,  and 
make  the  current  again. 

With  careful  work,  it  will  be  shown  that  with 


STIMULATION   OF   MUSCLE    AND   NERVE        157 

descending  currents,  the  first  contraction  will 
be  on  closure  only.  With  ascending  currents, 
the  first  contraction  will  be  on  opening  the 
current. 

The  explanation  is  that,  with  currents  which 
pass  through  the  sartorius  from  end  to  end 
the  point  of  greatest  density  is  the  smaller, 
lower  end.  This  is  cathodal  in  descending 
currents,  anodal  in  ascending  currents. 

Effect  of  the  Angle  at  which  the  Current 
Lines  cut  the  Muscle  Fibres 

Connect  non-polarizable  electrodes  through 
a  key  with  a  dry  cell.  Build  on  a  glass  plate 
with  normal  saline  clay  two  parallel  walls  a 
little  longer  than  the  sartorius  muscle  and 
one  centimetre  apart.  Join  the  ends  with 
wax,  to  make  a  rectangular  trough.  Eemove 
a  sartorius  muscle  from  a  curarized  frog, 
avoiding  all  injury  to  the  muscle.  Place  the 
muscle  in  the  trough,  and  cover  it  with  normal 
saline  solution.  Bring  a  non-polarizable  elec- 
trode against  the  centre  of  each  long  side,  so 
that  the  current  lines  shall  cut  the  muscle 
fibres  at  right   angles.     Close  the  key. 

There  will  be  no  contraction.  The  muscle  is 
inexcitable  to  currents  that  cross  its  fibres  at 
right  angles. 


158      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

Alter  the  angle  by  moving  one  electrode  to 
the  right,  the  other  to  the  left,  and  repeat  the 
experiment. 

The  stimulating  effect  will  increase  as  the 
angle  between  current  lines  and  the  long  axis  of 
muscular  fibres  diminishes. 

Nerves  also  are  inexcitable  to  transverse  cur- 
rents. Differences  in  resistance  play  a  great 
part  here.  The  resistance  of  nerves  is  said  to 
be  2  J  million  times  that  of  mercury,  when  the 
current  passes  along  the  nerve,  and  12J  million 
times  when  it  passes  transversely. 


The  Induced  Current 

The  break  induction  current,  owing  to  its  rapid 
rise  from  zero  to  maximum  intensity,  is  a  more 
effective  physiological  stimulus  than  the  make 
current,  and  may  therefore  be  chosen  for 
experimentation. 

1.  The  direction  of  the  induction  current  in 
the  secondary  coil  is  most  easily  determined 
electrolytically. 

Arrange  the  inductorium  for  maximal  currents. 
Bring  wires  from  the  posts  on  the  secondary  coil 
to  a  piece  of  filter  paper  wet  with  starch  paste 
containing  iodide  of  potassium.  Exclude  the 
make   currents    with   the    short-circuiting   key ; 


STIMULATION    OF    MUSCLE    AND   NERVE        159 

pass  the  maximal  break  currents  through  the 
electrolyte. 

Iodine  will  be  set  free  at  the  anode  and  will 
combine  with  the  starch  to  form  blue  iodide  of 
starch. 

Mark  the  positive  post  on  the  secondary  coil 
with  a  plus  sign. 

2.  Connect  the  poles  of  the  secondary  coil 
through  a  pole-changer  with  non-polarizable 
electrodes.  Make  a  nerve-muscle  preparation. 
Tie  a  ligature  about  the  nerve  about  two  cen- 
timetres from  the  central  end.  Place  one  elec- 
trode on  each  side  of  the  ligature.  The  passage 
of  a  nerve  impulse  from  the  central  electrode 
to  the  muscle  will  be  prevented  by  the  lig- 
ature, although  the  electric  current  can  still 
pass  between  the  electrodes.  Turn  the  pole- 
changer  so  that  the  electrode  on  the  periph- 
eral (muscle)  side  of  the  ligature  shall  be  first 
the  anode  and  then  the  cathode,  and  test  the 
irritability  to  weak  induction  currents,  begin- 
ning with  the  secondary  coil  some  distance  from 
the  primary,  and  gradually  increasing  the  intensity. 

Only  cathodal  stimulation  will  produce  con- 
traction. The  same  result  can  be  secured  by 
separating  the  cathode  and  anode  with  ammonia. 
If  the  nerve  is  painted  with  ammonia  in  the 
intrapolar  region,  break  currents  cease  to  cause 


160      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

contraction  when  the  cathode  is  on  the  central 
side  of  the  painted  zone.  Painting  the  cathodal 
region  directly  also  prevents  excitation. 

The  failure  of  the  induction  current  to  stimu- 
late at  the  anode,  on  opening  the  current,  is  due 
to  the  exceedingly  brief  duration  of  the  induced 
current;  there  is  not  time  for  a  sufficient  anelec- 
trotonic  alteration  in  excitability.  If  the  current 
is  shortened  still  more  (if  it  be  less  than  0.0015 
sec),  the  cathodal  excitation  also  disappears. 
With  very  strong  currents,  however,  opening  the 
current  stimulates  as  well  as  closure. 

3.  Additional  evidence  of  polar  action  is 
secured  by  connecting  the  electrodes  with  the 
capillary  electrometer  through  a  closed  short- 
circuiting  key.  The  meniscus  is  brought  into 
the  field,  the  nerve  is  stimulated  repeatedly 
with  maximal  break  currents,  and  then  stimu- 
lation is  stopped,  and  the  short-circuiting  key 
in  the  electrometer  circuit,  opened.  The  menis- 
cus will  move  in  a  direction  indicating  a  higher 
potential  at  the  anode  (positive  anodal  polariza- 
tion current). 

4.  Finally,  it  may  be  added  that  the  galvanic 
current  may  increase  the  stimulating  effect  of  the 
induced  current  as  pointed  out  on  page  80,  but  only 
when  the  cathode  of  the  induced  current  falls  ir: 
the  cathodal  region  of  the  polarizing  current. 


STIMULATION    OF   MUSCLE    AND   NERVE        161 

The  law  of  polar  excitation  holds  good  then 
for  the  induced  as  well  as  the  galvanic  current. 
In  fact,  there  is  no  essential  difference  between 
the  physiological  effects  of  induced  currents  and 
very  brief  galvanic  currents. 

Increasing  the  intensity  of  the  induced  cur- 
rent increases  at  first  the  excitation  (height  of 
contraction).  At  length,  however,  with  ascend- 
ing currents,  a  point  is  reached  beyond  which 
further  increase  in  strength  is  followed  first  by 
the  diminution  and  at  length  by  the  disappear 
ance  of  contraction.  With  still  higher  intensi- 
ties, the  contractions  reappear.  This  gap  in  the 
contraction  series  is  explained  by  the  increasing 
depression  of  irritability  at  the  anode  blocking 
the  cathodal  impulse ;  when  the  intensity  is  still 
further  increased,  the  opening  of  the  current  acts 
as  a  stimulus.  A  similar  result  may  be  secured 
with  the  galvanic  current. 

Apparatus 

Normal  saline.  Bowl.  Pipette.  Towel.  Simple  key. 
Non-polarizable  electrodes.  Nerve  holder.  Potter's  clay 
mixed  with  0.6  per  cent  solution  of  sodium  chloride. 
Saturated  solution  of  zinc  sulphate.  Muscle  clamp. 
Stand.  13  wires.  Kymograph.  Glazed  paper.  Two 
muscle  levers.  Thread.  Eheochord.  Two  dry  cells. 
Moist  chamber.  Glass  plate.  Ice.  Paraffin  paper.  Cork 
clamp.    Pole-changer.    Beaker.    Tripod,    Sodium  chloride. 

11 


162      GENERAL    TKOPERTIES    OF   LIVING   TISSUES 

Inductorium.  Electrodes.  Bunsen  burner.  Intestine  of 
a  rabbit.  Electromagnetic  signal.  Tuning  fork.  Brass 
electrodes.  Fine  copper  wire.  Frog  board.  2  pairs  •  of 
metal  electrodes,  each  passed  through  cork.  Electrom- 
eter. Paramecia.  Microscope.  Glass  slide.  Bent  hooks. 
One  per  cent  solution  of  veratrine  acetate.  Fine  glass 
pipette.  Filter  paper  saturated  with  starch  paste  con- 
taining potassium  iodide.  Frogs.  Fine  rubber  tubing 
for  insulating  electrodes.  Ammonia.  One  per  cent  solu- 
tion of  acid  potassium  phosphate.  Two  per  cent  solution 
of  sodic  carbonate.     Ligatures.     Filter  paper. 


CHEMICAL   AND    MECHANICAL    STIMULATION       163 


CHEMICAL  AND   MECHANICAL   STIMULATION 

Chemical  Stimulation 

The  contractility,  heat  production,  and  other 
phenomena  of  the  life  of  muscle  rest  at  base  on 
chemical  processes.  Anything  that  sufficiently 
alters  these  processes  may  be  a  stimulus.  A  most 
important  source  of  stimulation  is  the  alteration 
of  the  chemical  composition  of  muscle  through 
osmosis. 

Effect  of  Distilled  Water.  —  Place  a  sartorius 
muscle  in  distilled  water. 

Irregular  contractions  usually  occur.  The 
muscle  soon  swells,  and  becomes  white,  turbid, 
cadaveric. 

These  striking  changes  depend  on  the  with- 
drawal of  certain  bodies  by  osmosis.  Muscle 
contains  large  quantities  of  proteid,  particularly 
proteids  of  the  globulin  class ;  certain  carbo- 
hydrates, such  as  glycogen ;  nitrogenous  and 
other  extractives  ;  water ;  and  a  number  of  in- 
organic salts.  Most  of  these  bodies  are  largely 
or  wholly  insoluble  in  water,  and  require  for 
their   solution  the   presence  of  inorganic  salts. 


164      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

The  globulins,  for  example,  are  insoluble  in  dis- 
tilled water,  but  soluble  in  dilute  solutions  of 
sodium  chloride.  The  osmosis  of  salts  into  the 
distilled  water  in  the  above  experiment  first 
stimulates  and  then  destroys  the  contractility 
of  the  muscle. 

An  increase  in  the  saline  content  of  the  muscle 
juice  or  "plasma"  also  acts  as  a  stimulus,  and,  if 
excessive,  may  be  fatal. 

Strong  Saline  Solutions.  —  Place  a  sartorius 
muscle  on  a  slightly  inclined  glass  plate.  Cover 
the  lowest  fourth  of  the  muscle  with  crystals  of 
sodium  chloride. 

Irregular  contractions  will  appear. 

Drying.  —  The  effect  of  loss  of  water  is  best 
shown  in  nerve. 

Let  the  nerve  of  a  nerve-muscle  preparation 
dry.  Note  the  twitching  of  the  muscle  as  the 
water  content  diminishes.  Test  the  irritability 
of  the  nerve  from  time  to  time  with  induction 
currents.  It  will  first  increase,  then  disappear 
as  the  nerve  dries. 

Wet  the  nerve  with  0.6  per  cent  sodium 
chloride  solution. 

The  irritability  will  reappear. 

To  keep  muscles  and  nerves  in  good  condition 
for  experimentation,  it  is  necessary  to  moisten 
them  with  a  solution  containing  the  inorganic 
salts  most  abundant  in  the  tissue-liquids  in  the 


CHEMICAL  AND   MECHANICAL   STIMULATION      165 

proportions  in  which  they  are  present  in  those 
liquids.  Practically,  a  0.6  per  cent  solution  of 
sodium  chloride  has  commonly  been  employed, 
in  the  case  of  the  frog.  Such  a  solution  is  said 
to  be  isotonic,  i.  e.  neither  giving  nor  taking 
water  from  the  tissue..  That  it  is  not  perfectly 
indifferent  appears  from  this  experiment. 

"Normal  Saline."  —  Allow  a  sartorius  muscle 
to  stand  half  an  hour  in  normal  saline  solution 
(0.6  per  cent  NaCl).  Eecord  its  contraction  in 
response  to  a  maximal  break  induction  current. 
In  place  of  a  simple  twitch,  a  prolonged  contrac- 
tion of  abnormal  height  and  duration  will  usually 
be  secured. 

Importance  of  Calcium.  —  Place  the  "  normal 
saline  "  sartorius  in  0.6  per  cent  sodium  chloride 
solution  containing  10  per  cent  of  saturated  solu- 
tion of  calcium  sulphate.  After  ten  minutes 
record  the  maximal  break  contraction. 

The  abnormal  contraction  will  have  disap- 
peared. 

Constant  Chemical  Stimulation  may  cause  Peri- 
odic Contraction.  —  Place  a  sartorius  muscle  in  a 
solution  of  5  grams  NaCl,  2  grams  Na2HP04,  and 
0.4  gram  Na2C03  in  one  litre  of  distilled  water. 

Usually  rhythmic  contractions  are  seen.  All 
contractile  substance  shows  a  tendency  to  peri- 
odic contractions  in  response  to  a  constant  stimu- 


166      GENERAL   PROPERTIES   OF  LIVING  TISSUES 

lus,  whether  chemical,  mechanical,  or  electrical. 
There  are  reasons  for  believing  that  the  rhythmi- 
cal contractions  of  the  heart  are  the  consequence 
of  a  constant  chemical  stimulus. 

Mechanical  Stimulation 

Stimulate  a  nerve  mechanically  by  pinching 
the  cut  end  with  forceps. 

No  change  will  be  seen  in  the  nerve,  but  the 
muscle  will  shorten,  and  then  relax. 

Mechanical  stimulation  has  the  advantage  that 
it  can  be  localized  accurately,  and  for  this  reason 
it  has  been  used  where  electrical  stimulation 
seemed  inapplicable.  Tetanomotors  have  been 
constructed  by  Heidenhain  and  others  to  give  a 
rapid  succession  of  slight  blows  upon  the  nerve. 

Sudden  pressure  on  a  muscle  or  sudden  exten- 
sion may  cause  contraction.  Sometimes  the 
whole  muscle  contracts,  sometimes  only  the 
portion  directly  stimulated. 

Idio-Muscular  Contraction.  — With  the  point 
of  the  seeker  stroke  the  diaphragm  and  other 
muscles  of  a  recently  killed  rat,  or  other  small 
warm-blooded  animal,  in  a  direction  at  right 
angles  to  the  course  of  the  fibres. 

A  wheal,  i.  e.  a  long-continued  shortening  and 
thickening  of  the  fibre  stimulated,  will  be  seen. 
If  the  animal  be  not  too  long  dead,  a  momentary 


CHEMICAL  AND   MECHANICAL   STIMULATION      167 

twitch  of  the  whole  of  the  fibre  stimulated  will 
precede  the  continued  local  contraction  or  wheal. 
The  same  phenomenon  is  seen  for  a  briefer 
time  on  sharp  mechanical  stimulation  of  muscles 
in  living  animals,  for  example,  the  wheals  raised 
by  the  blow  of  a  whip.  In  men  long  ill  of  wast- 
ing diseases,  e.  g.  phthisis,  the  idio-muscular  con- 
tractions appear  on  drawing  a  pencil  point  across 
the  muscles.  Direct  total  stimulation  of  frog's 
muscle,  especially  in  the  spring  months,  may  be 
followed  by  long  continued  contraction.  Fatigue, 
cold,  and  many  poisons,  such  as  veratrine,  favor 
the  prolongation  of  the  phase  of  shortening.  The 
idio-muscular  contraction  is  not  a  "  tetanus," 
i.  e.  not  a  prolonged  shortening  clue  to  successive 
contractions,  the  interval  between  which  is  too 
short  to  permit  of  relaxation,  but  a  prolonged 
single  contraction,  the  cause  of  which  lies  in  the 
muscle  and  not  in  the  nerve. 

Apparatus 

Normal  saline.  Bowl.  Pipette.  Towel.  Glass  plate. 
Distilled  water.  Sodium  chloride.  Solution  of  sodium 
chloride  (0.6  per  cent),  containing  10  per  cent  of  saturated 
solution  of  calcium  sulphate.  Solution  containing  5  grams 
sodium  chloride,  2  grams  di-sodium  hydrogen  phosphate, 
and  0.4  gram  sodium  carbonate,  in  1000  c.c.  water.  Small 
warm-blooded  animal  recently  killed.  Introduction  coil. 
Dry  cell.     Key.     Electrodes.     3  Wires.     Frogs. 


168      GENERAL   PROPERTIES   OF   LIVING   TISSUES 


VI 

IRRITABILITY   AND   CONDUCTIVITY 

Irritability  is  the  power  of  discharging  energy 
on  stimulation.  The  form  in  which  the  kinetic 
energy  of  muscle  appears  is  partly  mechanical 
work  (the  visible  contraction)  and  partly  molec- 
ular, —  heat,  chemical  action,  and  electricity. 
In  the  nerve,  the  kinetic  energy  is  wholly  molec- 
ular ;  an  electromotive  force  is  generated,  prob- 
ably heat  is  set  free  (though  this  statement  — 
which  is  based  simply  on  analogy  —  is  frequently 
disputed),  and  a  molecular  change  —  the  nerve 
impulse  —  arises  at  the  seat  of  stimulation.  In 
both  muscle  and  nerve,  by  virtue  of  their  con- 
ductivity, the  change  induced  by  stimulation  is 
as  a  rule  not  limited  to  the  region  stimulated,  but 
passes  in  both  directions  along  each  stimulated 
fibre.  In  neither  muscle  nor  nerve  can  the 
changes  in  energy  spread  transversely  ;  they  are 
limited  to  the  muscle-  or  nerve-fibre  in  which 
they  arise. 

It  will  be  shown  that  conductivity  and  irrita- 
bility are  essentially  different  functions. 


IRRITABILITY  AND    CONDUCTIVITY  1G9 

The   Independent   Irritability   of  Muscle.  —  The 

stimulus  that  causes  the  contraction  of  a  muscle 
may  be  applied  either  to  the  nerve  or  to  the 
muscle  itself.  If  to  the  nerve,  the  muscle  will 
be  thrown  into  the  active  state  not  by  the  origi- 
nal stimulus,  but  by  a  nerve  impulse.  If  to  the 
muscle,  the  nerve  will  still  be  stimulated,  for 
examination  shows  terminal  fibres  distributed,  in 
skeletal  muscle  at  least,  probably  to  every  fibre, 
and  with  few  exceptions  to  all  parts  of  the 
muscle.  The  fact  that  muscles  may  contract 
when  an  electric  current  flows  through  them,  or 
when  otherwise  stimulated,  does  not  therefore  of 
itself  indicate  that  electricity  is  a  stimulus  to 
muscle  protoplasm.  Before  this  can  be  estab- 
lished, it  will  be  necessary  to  demonstrate  con- 
traction in  parts  of  muscle  not  provided  with 
nerves ;  for  example,  the  distal  part  of  the  sar- 
torius,  or  in  muscles  in  which  the  nerves  have 
been  destroyed  by  curare  or  by  degeneration. 

Nerve-free  Muscle.  —  Beniove  the  sartorius 
muscle,  together  with  the  portion  of  the  pelvis 
and  the  tibia  to  which  the  muscle  is  attached, 
and  lay  it  on  a  glass  plate.  Stimulate  the  distal 
(tibial)  fifth,  in  which  examination  with  the 
microscope  would  show  the  absence  of  nerve 
fibres,  with  a  strong  break  induction  current. 

The  nerve-free  muscle  will  contract. 


170      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

Muscle  with  Nerves  Degenerated.  —  A  nerve 
fibre  severed  from  its  cell  of  origin  dies  or  "  de- 
generates "  down  to  its  ultimate  endings.  Expose 
the  sciatic  nerve  in  the  middle  of  the  thigh  of  a 
frog  in  which  the  nerve  has  been  severed  near 
the  pelvis  ten  days  before,  so  that  the  whole  of 
the  nerve  distal  to  the  section  shall  have  degen- 
erated.    Stimulate  the  degenerated  trunk. 

No  contraction  is  seen  in  the  muscles  of  the 
leg.     Stimulate  the  muscles  directly. 

Contraction  takes  place. 

The  Nerve-free  Embryo  Heart.  —  Embryological 
studies  show  that  the  nerves  of  the  heart  are 
formed  from  epiblast  in  the  walls  of  the  neural 
canal,  and  do  not  grow  into  the  heart  until  the 
close  of  the  third  day  of  incubation  (chick). 
The  heart,  however,  begins  to  beat  during  the 
second  day  of  embryonic  life,  before  even  the 
blood  which  it  shall  pump  is  formed.  Thus 
the  heart  muscle,  in  the  embryo,  is  capable  of 
contraction  in  the  absence  of  nerves. 

Cover  an  egg  which  has  been  incubated  60-70 
hours  with  0.75  per  cent  solution  of  sodium 
chloride  warmed  to  38°  C.  Eemove  the  shell 
with  the  forceps  over  one  third  of  the  egg,  be- 
ginning at  the  broad  end,  and  leaving  the  shell 
membrane  behind.  Now  remove  the  shell  mem- 
brane.    Note  the  buating  heart. 


IRRITABILITY   AND    CONDUCTIVITY  171 

Paralysis  of  Nerve  Endings  with  Curare.  — 
Make  two  nerve  muscle  preparations  A  and  B, 
and  fill  two  watch  glasses  with  curare  solution. 
In  one  watch  glass  lay  the  nerve  trunk  of  prep- 
aration A  and  in  the  other  watch  glass  the  muscle 
of  preparation  B.  Cover  muscle  A  and  nerve  B 
with  filter  paper  moistened  with  normal  saline 
solution,  to  prevent  drying.  At  intervals  of  ten 
minutes  stimulate  nerve  B  with  induction 
currents. 

When  the  poison  has  acted  the  stimulation  of 
nerve  B  will  produce  no  contraction  of  the  at- 
tached muscle,  which  lies  in  the  curare.  Either 
the  muscle  or  the  nerve  has  been  poisoned. 

Stimulate  muscle  B  directly. 

It  contracts.  Hence  the  curare  has  poisoned 
the  nerve ;  probably  the  terminals  of  the  nerve 
within  the  muscle. 

Now  remove  nerve  A  from  the  curare  and 
stimulate  the  trunk  of  the  nerve. 

The  attached  muscle  will  contract.  Hence 
the  trunk  of  the  nerve  has  not  been  poisoned 
by  the  curare. 

It  follows  that  curare  poisons  the  endings  of 
the  nerve  within  the  muscle.  Therefore,  the 
contraction  of  muscle  B,  in  which  the  nerve  end- 
ings were  paralyzed,  must  have  been  due  to  the 
independent  irritability  of  the  muscle  fibres. 


172      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

The  occurrence  of  idio-muscular  contraction 
(see  page  166)  is  an  additional  proof  of  the 
independent  irritability  of  muscle. 

Irritability  and  Conductivity  are  Separate  Prop- 
erties of  Nerve.  —  1.  Carbon-dioxide.  —  Arrange 
the  inductorium  for  tetanizing  currents.  Connect 
the  secondary  coil  with  the  mam  posts  of  the 
pole-changer     (cross-wires    out).      Connect    the 


Fig.  42.  The  gas  chamber,  with  bottle  for  generating  carbon  dioxide, 
and  a  pole-changer  arranged  to  stimulate  the  nerve  either  within  or  without 
the  chamber.  The  holes  in  the  glass  through  which  the  nerve  passes  are 
plugged  with  normal  saline  clay. 

two  other  pairs  of  posts  with  the  usual  stimula- 
tion electrodes  and  the  electrodes  of  the  small 
gas  chamber  (Fig.  42).  Join  the  inflow  tube  of 
the  gas  chamber  with  the  outflow  tube  of  the 
carbon-dioxide  bottle.  The  gas  chamber  should 
rest  on  a  glass  plate.  Make  a  nerve-muscle 
preparation,  preserving  the  full  length  of  the 
sciatic  nerve  up  to   the   vertebral  column.     Tie 


IRRITABILITY   AND   CONDUCTIVITY  173 

a  silk  thread  to  the  extreme  end  of  the  nerve, 
and  fasten  the  thread  to  the  end  of  the  seeker 
by  a  drop  of  wax  cement.  With  the  aid  of  the 
seeker,  pass  the  thread  through  the  holes,  and 
draw  the  nerve  after,  so  that  the  nerve  lies  on 
the  electrodes.  The.  nerve  should  be  drawn 
through  until  the  muscle  is  close  to  the  gas 
chamber.  Stop  the  holes  through  which  the 
nerve  passes  with  normal  saline  clay.  Bring  the 
outer  pair  of  electrodes  against  the  central  end 
of  the  nerve  near  its  exit  from  the  gas  chamber. 
Determine  which  position  of  the  pole-changer 
corresponds  to  each  pair  of  electrodes.  Stimulate 
the  nerve  first  within  the  chamber,  and  then  on 
the  central  end  of  the  nerve,  using  a  current  just 
sufficient  to  cause  tetanus.  In  both  cases  tetanus 
will  result.  Now  pour  20  per  cent  hydrochloric 
acid  on  the  marble  in  the  generator.  After  the 
gas  has  passed  through  the  chamber  for  a  moment, 
stimulate  as  before. 

Stimulation  of  the  portion  of  the  nerve  exposed 
to  the  carbon-dioxide  is  no  longer  effective,  while 
stimulation  of  the  part  central  to  the  gas  chamber 
still  produces  tetanus. 

But  the  nerve  impulses  created  by  stimulation 
of  the  nerve  central  to  the  gas  chamber  cannot 
reach  the  muscle  except  by  passing  along  the 
nerve  and  through  the  carbon-dioxide.     The  con- 


174      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

ductivity  of  the  nerve  therefore  is  still  sufficient, 
while  the  irritability  has  been  suspended  by  the 
action  of  the  gas.  Hence,  conductivity  and  irri- 
tability are  by  no  means  interchangeable  terms. 

Their  essential  difference  is  further  shown  by 
the  effect  of  alcohol  vapor,  which  impairs  con- 
ductivity while  irritability  is  little  changed. 

2.  Alcohol.  — Disconnect  the  rubber  tube  from 
the  gas  generator,  and  blow  through  the  gas 
chamber  until  the  carbon-dioxide  is  driven  out. 
The  nerve  will  recover  its  irritability.  Deter- 
mine this  by  stimulating  from  time  to  time. 
When  the  nerve  has  recovered,  drop  a  little 
alcohol  through  the  long  glass  tube  of  the  gas 
chamber,  being  careful  that  only  the  vapor  of 
the  alcohol  comes  into  contact  with  the  nerve. 
Stimulate  both  within  and  central  to  the  chamber. 

After  a  time,  tetanus  will  no  longer  be  pro- 
duced by  stimulating  central  to  the  chamber. 
Stimulation  within  the  latter  is  still  effective. 
Thus  conductivity  is  impaired,  while  irritability 
remains  intact,  or  at  least  is  affected  to  a  less 
extent.  (The  electrodes  within  the  alcohol  at- 
mosphere should  not  be  too  far  from  the  opening 
through  which  the  nerve  passes  to  the  muscle, 
else  the  loss  of  conductivity  in  this  part  of  the 
nerve  may  make  difficult  the  demonstration  of 
irritability.) 


IRRITABILITY   AND    CONDUCTIVITY  175 

Minimal  and  Maximal  Stimuli  ;  Threshold  Value. 
—  Arrange  the  gastrocnemius  muscle  to  write  on 
a  smoked  drum.  Connect  one  binding  post  of 
the  secondary  coil  to  the  muscle  clamp,  the 
other  binding  post  to  the  post  on  the  muscle 
lever.  Load  the  muscle  with  10  grams.  De- 
scribe an  abscissa  on  the  smoked  paper,  turning 
the  drum  by  hand.  Send  a  feeble  break  induc- 
tion current  through  the  muscle. 

There  will  be  no  response. 

Eepeat  the  break  currents,  gradually  moving 
the  secondary  closer  to  the  primary  coil. 

At  a  certain  point  the  muscle  will  just  con- 
tract ("  threshold  value  ").  This  is  a  minimal 
contraction  produced  by  a  minimal  stimulation. 

Turn  the  drum  5  mm.,  move  the  secondary 
coil  5  mm.  nearer  the  primary,  send  in  another 
break  current,  and  record  the  contraction.  Con- 
tinue this. 

The  contraction  in  answer  to  each  break  cur- 
rent increases  with  the  strength  of  the  currents 
at  first  rapidly,  then  slowly,  up  to  a  certain  point. 
Further  increase  in  the  strength  of  the  stimulus 
produces  no  further  increase  of  contraction.  The 
stimulus  and  the  resulting  contraction  have  now 
become  maximal. 

There  is  a  striking  disproportion  between  the 
energy    of   the  stimulus   necessary    to   throw  a 


176      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

nerve  or  muscle  into  the  active  state,  and  the 
energy  that  the  stimulus  sets  free.  It  is  as  if  a 
spark  fell  into  powder;  the  active  process  is  to 
be  regarded,  with  some  reservations,  as  an  explo- 
sion. But  only  a  part  of  the  latent  energy  of 
muscle  can  be  set  free  by  any  one  stimulus. 

Threshold  Value  Independent  of  Load.  —  Re- 
peat the  preceding  experiment,  and  load  the 
muscle  with  50  grams  instead  of  10. 

The  threshold  value  will  not  be  changed. 

Summation  of  Inadequate  Single  Stimuli.  — 
Place  the  secondary  coil  of  the  inductorium  at 
such  a  distance  from  the  primary  that  a  break 
current  shall  be  nearly,  but  not  quite  sufficient 
to  cause  a  contraction.  Let  the  muscle  rest 
without  stimulation  for  about  a  minute.  Repeat 
the  inadequate  single  stimulation  at  intervals  of 
five  seconds.     No  curve  need  be  written. 

After  a  time,  contraction  will  be  secured. 

The  excitation  outlasts  the  stimulus,  and  rein- 
forces subsequent  stimuli :  finally,  the  summed 
excitations  call  forth  a  contraction.  Summation 
is  of  frequent  occurrence  probably  in  all  living 
tissues. 

Relative  Excitability  of  Flexor  and  Extensor 
Nerve  Fibres  ;  Ritter-Rollett  Phenomenon.  —  Ex- 
pose the  sciatic  nerve  in  a  brainless  frog  in 
the  pelvic  region.     Set  the  hammer  of  the  in- 


IRRITABILITY    AND    CONDUCTIVITY  177 

ductorium  in  action  (binding  posts  2  and  3), 
and  stimulate  the  nerve  with  weak  induction 
currents. 

The  leg  will  be  flexed. 

Use  stronger  induction  shocks. 

As  the  intensity  increases  extension  as  well  as 
flexion  is  seen.  A  still  further  increase  causes 
extension  only. 

The  gradations  of  intensity  necessary  to  show 
these  results  are  sometimes  difficult  to  secure. 
The  phenomenon  of  relative  excitability  is  not  lim- 
ited to  the  case  just  cited.  Weak  stimulation  of 
the  vagus  causes  adduction  of  the  vocal  bands  ; 
stronger  stimulation,  abduction.  Weak  stimula- 
tion causes  opening  of  the  claw  of  the  lobster,  while 
stronger  stimulation  of  the  same  nerve  causes  clo- 
sure. Weak  stimulation  of  the  hypoglossal  nerve 
in  the  dog  and  rabbit  causes  the  tongue  to  be  thrust 
from  the  mouth,  while  with  strong  stimulation  the 
tongue  is  withdrawn  into  the  mouth.  It  must  not 
be  forgotten  that  the  anatomical  nerves  stimulated 
in  these  experiments  are  composed  of  many  axis 
cylinders,  each  of  which  is  a  physiological  nerve. 
That  they  should  vary  in  excitability  is  to  be 
expected. 

A  second  and  probably  better  explanation  of 
the  Eitter-Eollett  phenomena  is  found  in  the  dif- 
ference in  structure  of  the  flexors  and  extensors. 

12 


178      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

Muscle  fibres  consist  of  contractile  substance  im- 
bedded in  sarcoplasm.  The  relation  between 
the  contractile  substance  differs  in  the  same 
muscle  in  different  species  and  individuals,  and 
differs  further  in  the  muscles  of  the  same  indi- 
vidual. In  striated  muscles  of  vertebrates,  those 
rich  in  sarcoplasm  have  a  turbid,  opaque  appear- 
ance, while  those  poor  in  sarcoplasm  are  translu- 
cent. Important  differences  in  contractility, 
irritability,  etc.,  depend  on  this  difference  of 
structure.  Muscles  which  contain  many  u  clear" 
fibres  (poor  in  sarcoplasm)  are  more  irritable 
than  those  containing  many  of  the  fibres  rich  in 
sarcoplasm.  In  the  flexors  of  the  frog  the  "  clear  " 
fibres  are  relatively  more  numerous  than  in  the 
extensors. 

Specific  Irritability  of  Nerve  Greater  than  that 
of  Muscle.  —  Arrange  an  inductorium  for  single 
induction  currents.  Make  as  rapidly  as  possible 
two  nerve-muscle  preparations,  A  and  B.  Bring 
a  wire  from  the  secondary  coil  to  each  end  of 
muscle  A.  Let  the  nerve  of  B  rest  on  muscle  A. 
No  stimulation  can  now  reach  B  except  through 
that  part  of  the  nerve  of  B  which  rests  on  muscle 
A.  Place  the  secondary  some  distance  from  the 
primary  coil.  Stimulate  muscle  A  with  make 
induction  shocks,  the  strength  of  which  is  gradu- 
ally increased  by  approximating  the  coils. 


IRRITABILITY   AND    CONDUCTIVITY  179 

Muscle  B,  which  is  stimulated  only  through 
its  nerve,  will  contract  before  muscle  A,  which 
is  stimulated  directly.  Hence,  the  specific  irri- 
tability of  nerve  is  greater  than  that  of  muscle, 
provided  (1)  that  the  intensity  of  the  stimulating 
current  is  equal  for  both  nerve  and  muscle,  and 
(2)  that  the  irritability  of  the  two  muscles  does  not 
differ,  and  (3)  that  the  stimulation  of  the  nerve 
of  B  is  not  by  unipolar  induction.  The  first 
source  of  error  may  be  excluded,  because  the 
density  of  the  current  passing  through  the  por- 
tion of  nerve  lying  on  muscle  A  is  certainly  not 
greater  than  the  density  of  the  current  passing 
through  the  muscle  itself.  The  second  possibil- 
ity is  tested  as  follows  :  — 

Eeverse  the  muscles  and  repeat  the  experi- 
ment. 

The  result  will  not  be  altered. 

The  third  source  of  error  is  excluded  as  follows. 

Tie  a  ligature  about  the  nerve  of  B,  between 
muscles  A  and  B.  The  physiological  conduc- 
tivity of  nerve  B  is  thereby  destroyed,  and  the 
nerve  impulse  cannot  pass ;  but  the  physical  con- 
tinuity of  the  nerve,  and  hence  its  power  to  con- 
duct electricity,  is  still  present. 

The  strongest  induction  currents  applied  to 
muscle  A  will  now  fail  to  produce  contraction 
of  B. 


180      GENERAL    PROPERTIES    OF   LIVING   TISSUES 

Irritability  at  Different  Points  of  Same  Nerve.  — 
Determine  the  threshold  value  for  the  sciatic 
nerve  near  the  gastrocnemius  muscle  and  about 
two  centimetres  from  the  cut  end  of  the  nerve. 

The  farther  from  the  muscle  the  nerve  is  stim- 
ulated, the  lower  will  be  the  threshold  value.  It 
has  been  suggested  in  explanation  of  this  that 
the  nerve  impulse  gathers  force  as  it  passes 
along  the  nerve,  and  is  the  more  powerful  the 
longer  the  nerve  which  it  traverses  (avalanche 
theory).  It  has  also  been  suggested  that  the 
nearer  to  the  nutrient  cell  of  origin  the  stim- 
ulus is  applied,  the  greater  the  effect.  The  true 
explanation  lies  in  the  fact  that  the  irritability 
of  the  nerve  is  raised  in  the  neighborhood  of  the 
cross-section  by  the  passage  of  the  demarcation 
current  through  that  portion,  as  explained  on 
page  296.  Tigerstedt  has  shown  with  mechani- 
cal stimuli  that  the  uninjured  nerve  has  equal 
irritability  throughout. 

The  Excitation  Wave  remains  in  the  Muscle  or 
Nerve  Fibre  in  which  it  starts.  —  In  order  to 
limit  the  stimulus  to  one  or  two  fibres,  the 
method  of  unipolar  stimulation  may  be  adopted. 

Fasten  in  one  post  of  the  secondary  coil  of 
the  inductorium  arranged  for  tetanizing  currents 
a  wire  soldered  to  a  blunt  needle.  The  needle, 
except  near  the  free  end,  and  the  lower  part  of 


IRRITABILITY   AND   CONDUCTIVITY  181 

the   connecting   wire,  should   be   inclosed   in   a 
glass  tube  for  insulation. 

Expose  the  sacral  plexus  in  a  brainless  frog  in 
which  the  skin  has  been  removed  from  the  hind 
limbs.  Connect  the  preparation  by  means  of  a 
copper  wire  with  the  earth  through  the  gas  or 
water  pipes. 

Touch  the  sacral  nerves  here  and  there  with 
the  needle  electrode,  watching  meanwhile  the 
sartorius  muscle. 

Partial  contractions  will  be   seen  in  the  sar- 
torius,  now  of  the  inner,  now  the  outer  fibres, 
according  to  the  nerve  fibres  touched 
by  the  needle. 

Stimulate  the  sartorius  directly. 
Only   the    fibres    touched    by   the 
needle  contract. 

Evidently  the  excitation  wave  re- 
mains limited  both  in  the  muscle 
and  the  nerve  to  the  fibres  in  which 

sartorius.         It  Starts. 

The  same  Nerve  Fibre  may  conduct  Impulses 
both  Centripetally  and  Centrifugally.  —  1.  The 
nerve  of  the  sartorius  divides  at  the  muscle,  part 
going  to  each  half  of  the  muscle  (Fig.  43). 
Microscopical  examination  shows  that  the  divi- 
sion is  not  simply  a  parting  of  individual  nerve 
fibres,   but   that   each    axis    cylinder   forks,  one 


182      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

limb  going  upwards,  the  other  downwards.  If 
the  muscle  be  severed  between  the  forks,  no 
impulse  started  in  one  half  of  the  muscle  could 
reach  the  other  half,  except  by  going  up  one 
branch  to  the  original  axis  cylinder  and  down 
the  remaining  branch ;  for  it  is  known  that  the 
nerve  impulse  does  not  escape  transversely  from 
one  axis  cylinder  to  other  neighboring  ones. 

Eemove  a  sartorius  muscle  with  great  care. 
Split  the  muscle  in  the  middle  line  for  one  third 
of  its  length,  beginning  at  the  broad  end,  as  in- 
dicated in  the  diagram.  Stimulate  the  muscle 
fibres  of  the  right  segment  mechanically,  by 
snipping  the  preparation  with  scissors  in  the 
line  a.     Do  not  cut  quite  through  the  segment. 

Only  the  right  half  twitches. 

Eepeat  'the  stimulus  by  snipping  in  the  line  av 

Again  only  the  right  half  twitches. 

Stimulate  in  the  line  b. 

Both  segments  twitch,  or  at  least  some  fibres 
in  each. 

Repeat  at  bv 

Both  segments  twitch  again. 

2.  The  gracilis  of  the  frog  is  divided  into  an 
upper,  shorter  part  and  a  lower,  longer  part  by 
a  tendon  (Fig.  44,  j).  Each  axis  cylinder  in 
the  nerve  N,  on  approaching  the  muscle,  divides 
into    two    branches,  one  of   which    goes    to    the 


IRRITABILITY   AND    CONDUCTIVITY 


183 


Fig.  ±i.    The  gracilis. 


upper  and  the  other  to  the  lower  portion  of  the 
muscle. 

Eemove  the  muscle  together  with  a  portion  of 
its  attached  nerve,  and  examine 
the  inner  surface  (Fig.  .  44). 
The  nerve  (N)  divides  into  two 
branches,  of  which  the  upper 
(K)  runs. to  the  shorter  portion 
of  the  muscle  and  is  mibranched 
for  some  distance,  while  the 
other  (L)  has  a  very  short  stem 
and  sinks  almost  at  once  into  the 
substance  of  the  lower  part.  One  of  the  branches 
(H)  perforates  the  muscle  and  goes  to  the  skin. 

With  a  sharp 
pair  of  scissors  cut 
out  entirely  the  part 
shaded  in  the  dia- 
gram, without  in- 
juring the  nerves. 
The  halves  of  the 
muscle  are  now 
united  only  by  the 
forked  nerve. 

Stimulate  the  end  branches  of  the  nerve  in 
one  of  the  pieces  of  muscle  by  snipping  with 
scissors ;  also  chemically,  with  a  lump  of  salt. 

Both  pieces  will  contract. 


Fig.  45. 


184      GENERAL   PROPERTIES    OF   LIVING   TISSUES 

Speed  of  Nerve  Impulse.  —  Smoke  a  drum,  and 
adjust  it  for  "  spinning."  Place  two  pairs  of 
needle  electrodes  in  corks  in  the  moist  chamber. 
Arrange  the  inductorium  for  maximal  make 
currents,  placing  a  simple  key  and  the  electro- 
magnetic signal  in  the  primary  circuit  (Fig.  45). 
Connect  the  secondary  coil  to  the  side  cups  of 
the  pole-changer.  Connect  the  end  pairs  of 
cups  each  with  one  pair  of  the  electrodes  in 
the  moist  chamber.  Make  a  nerve-muscle  prep- 
aration, preserving  the  full  length  of  the  sciatic 
nerve.  Fasten  the  femur  in  the  clamp  in  the 
moist  chamber.  Connect  the  Achilles  tendon 
to  the  muscle  lever.  Bring  the  point  of  the 
lever  against  the  drum  immediately  over  the 
writing  point  of  the  electro-magnetic  signal. 
Let  the  nerve  rest  on  the  electrodes,  one 
pair  near  the  end  of  the  nerve,  the  other 
near  the  muscle.  Spin  the  drum  slowly. 
Hold  the  writing  point  of  a  vibrating  tuning 
fork  against  the  smoked  paper  beneath  the 
line  drawn  by  the  signal.  Send  a  maximal 
induction  current  through  first  one  pair  of  elec- 
trodes and  then  the  other.  Determine  the  inter- 
val between  the  moment  of  stimulation  and 
the  beginning  of  contraction  in  each  instance. 
[This  is  done  by  turning  the  drum  back  until 
the  writing  point  of  the  signal  lies  precisely  in 


IRRITABILITY   AND    CONDUCTIVITY  185 

the  vertical  line  marked  by  it  when  the  current 
was  made,  and  then  stimulating  the  muscle  to 
contract.  The  ordinate  drawn  by  the  muscle 
lever  (the  drum  being  still  at  rest)  will  be 
synchronous  with  the  ordinate  drawn  by  the 
signal  during  the  experiment.] 

It  will  be  found  that  the  interval  between 
stimulation  and  contraction  is  greater  when  the 
nerve  is  stimulated  far  from  the  muscle  than  it 
is  on  stimulation  near  the  muscle.  The  differ- 
ence is  the  time  occupied  by  the  passage  of  the 
excitation  wave  along  the  nerve  between  the 
electrodes. 

Measure  the  length  of  nerve  between  the  elec- 
trodes, and  calculate  the  speed  of  the  nerve  im- 
pulse per  second. 

It  is  assumed  in  this  method  that  the  interval 
between  the  closure  of  the  primary  circuit  and 
the  beginning  of  the  nerve  impulse  is  the  same 
in  both  instances,  and  that  the  interval  between 
the  arrival  of  the  impulse  in  the  muscle,  and  the 
visible  change  of  form,  is  likewise  the  same  in 
both.  If  the  mean  and  the  probable  deviation  of 
a  series  of  measurements  are  taken,  a  fairly  accu- 
rate result  may  be  expected.  A  better  method, 
however,  is  to  record  the  passage  of  the  negative 
variation  over  a  measured  length  of  nerve  by 
photographing   the    meniscus    of    the    capillary 


186      GENERAL   PROPERTIES   OF  LIVING  TISSUES 

electrometer.       Similar    measurements    can    be 
made  with  a  differential  rheotome  (page  313). 

Helmlioltz  found  in  motor  nerves  of  the  frog 
an  average  speed  of  27  metres  per  second,  but 
the  individual  variation  is  considerable.  The 
speed  is  very  slow  compared  with  that  of  light,  or 
even  sound.  It  is  modified  by  changes  in  tem- 
perature, nutrition,  anaesthetics  (alcohol,  ether, 
chloroform,  carbon  dioxide),  the  intensity  of  the 
stimulus,  —  above  a  certain  value,  the  greater 
the  stimulus,  the  more  rapid  the  conduction,  — 
and  by  many  other  factors.  Specific  differences 
are  found  depending  on  the  structure  of  the 
nerve.  Thus  the  velocity  has  been  found  in  mam- 
malian nerve  to  smooth  muscle  to  be  about  9 
metres  per  second,  while  in  the  bivalve  Anodonta 
it  is  said  to  be  only  1  centimetre  per  second. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Dry  cell.  Inductorium.  Key.  Wires.  Frog  with  sci- 
atic nerve  degenerated.  Hen's  egg  incubated  60-70  hours. 
NaCl  solution  (0.75%).  Ligatures.  Filter  paper.  One 
per  cent  solution  of  curare.  Pole-changer.  Gas  chamber. 
Carbon  dioxide  generator.  Twenty  per  cent  hydrochloric 
acid.  Broken  marble.  Alcohol.  Muscle  clamp.  Stand. 
Muscle  lever  with  scale  pan.  Millimetre  rule.  Ten  gram 
weights.  Needle  electrodes  (glass  tube).  Moist  chamber. 
Two  pairs  of  non-polarizable  electrodes.  Electro-magnetic 
signal.  Recording  drum.  Glazed  paper.  Tuning  fork. 
Normal  saline  clay. 


PART  II 

THE   INCOME   OF   ENERGY 


PART   II 
THE   INCOME   OF   ENERGY 

I  FERMENTATION 

Hydrolysis  of  Stakch  by  Diastase 

Conversion  of  Starch  to  Sugar  by  Germinating 
Barley.  —  To  5  grams  crushed,  germinating  barley 
add  10  grams  potato  starch,  and  20  c.c.  of  cold 
water.  Then  add  gradually  70  c.c.  of  hot  water 
with  constant  stirring.  Keep  the  mixture  in  a 
temperature  of  about  60°  C.  for  one  hour. 

The  insoluble  starch  will  be  converted  to  a 
sweet  liquid.1 

Boil  10  c.c.  of  Fehling's  solution,2  dilute  the 
syrup  with  water  and  add  it  drop  by  drop  to  the 
boiling  Fehling's  solution. 

1  Kirchoff  :  Schweigger's  Journal  fur  Chemie  und  Physik, 
1815,  xiv,  p.  389.  There  is  a  small  amount  of  sugar  and  starch 
in  the  barley  itself. 

2  Fehling's  solution.  —  In  a  large  watch  glass  weigh  34.639 
gms.  pure  cupric  sulphate  (clean  crystals).  Dissolve  the  crystals 
by  warming  them  with  about  150  c.c.  water  in  an  evaporating 
dish.  Place  the  solution  in  a  500-c.c.  measuring  flask.  Wash  the 
remnant  from  the  dish  into  the  flask.  Allow  the  liquid  to  cool 
completely.     Add  water  to  the  mark  on  the  neck  of  the  flask. 

Warm  about  173  gms.  potassium  sodium  tartrate  in  a  little 
water  until  dissolved.  Place  the  solution  in  a  500-c.c.  measur- 
ing flask,  add  100  c.c.  sodium  hydroxide,  sp.  gr.  1.34  (about 
31  per  cent),  and,  after  the  mixture  has  completely  cooled,  fill 
the  flask  to  the  mark  on  the  neck. 

In  use,  mix  equal  volumes  of  each  solution  in  a  dry  glass. 

One  molecule  grape  sugar  reduces  five  molecules  cupric  oxide 
to  cuprous  oxide  ;  10  c.c.  of  Fehling's  copper  sulphate  solution 
equals  0.05  gm.  grape  sugar. 


190  THE   INCOME   OF   ENERGY 

Eed  cuprous  oxide  or  its  yellow  hydrate  will 
separate. 

The  germinating  barley  causes  the  starch  to 
take  up  water,  thus  changing  to  a  reducing  sugar. 
In  this  instance  the  agent  is  a  living  cell,  or 
some  substance  or  "  ferment "  secreted  by  the 
cell.  It  is  now  necessary  to  inquire  whether 
ferments  are  separable  from  living  cells. 

Conversion  of  Starch  to  Sugar  by  Salivary  Dias- 
tase (Ptyalin).  —  To  10  c.c.  of  starch  paste1  col- 
ored blue  with  iodine  (blue  iodide  of  starch)  add 
about  2  c.c.  of  filtered  saliva  and  keep  the  mixture 
at  35-40°  C. 

The  starch  paste  will  liquefy  and  become  sweet. 
The  blue  color  will  become  lighter  and  finally 
disappear. 

Test  with  Fehling's  solution.  Eeduction  will 
take  place. 

Saliva  hydrolyzes  starch  to  a  reducing  sugar. 

Saliva  is  secreted  by  the  cells  in  the  salivary 
gland,  placed  some  distance  from  the  mouth. 
The  saliva  itself  contains  no  secreting  cells. 
There  are  ferments,  then,  which  act  at  a  distance 

1  Starch  paste.  —  Rub  1  gm.  potato  starch  in  a  mortar  with 
25  c.c.  cold  water.  Pour  the  mixture  into  an  evaporating  dish. 
Wash  the  remnant  from  the  mortar  and  pestle  into  the  dish  with 
75  c.c.  water.  Heat  the  mixture  to  boiling  point  with  constant 
stirring.  The  starch  paste  will  turn  blue  upon  addition  of  iodine 
(iodide  of  starch). 


FERMENTATION  191 

from  the  cells  that  produce  them.  There  seems 
thus  an  important  distinction  to  be  made  between 
organized  ferments,  those  acting  apparently  with- 
in the  living  cell,  and  unorganized  ferments,  like 
the  salivary  diastase,  which  is  secreted  by  a 
living  cell  but  remains  active  after  leaving  the 
cell.  It  will  be  seen  that  this  distinction  cannot 
be  maintained. 

Extraction  of  Diastase  from  Germinating  Barley.1 
—  Crush  freshly  germinating  barley  in  a  mortar 
with  about  half  its  weight  of  water.  Keep  the 
mass  two  hours  at  35-40°  C.  Squeeze  out  the 
watery  extract  in  a  press,  or  strain  by  strong 
pressure  through  a  linen  cloth.  Add  excess  of 
alcohol. 

Diastase  will  be  precipitated.  It  may  be  puri- 
fied by  dissolving  it  in  water  and  reprecipitating 
with  alcohol. 

Add  a  little  diastase  to  10  c.c.  starch  paste, 
colored  blue  with  iodine.  The  starch  will  be  con- 
verted to  sugar.     The  blue  color  will  disappear. 

It  appears,  therefore,  that  ferment  action  is 
not  dependent  on  the  life  of  the  cell  that  secretes 
the  ferment. 

Specific  Action  of  Ferments.  —  The  question 
now  arises   whether   the   diastase   acts   only  to 

1  Payen  and  Persoz :  Annates  de  chimie  et  de  physique, 
1833,  liii,  p.  78. 


192  THE   INCOME    OF   ENERGY 

change  starch  to  sugar  or  whether  it  causes  the 
decomposition  of  other  substances. 

Place  a  small  piece  of  fibrin  in  a  test-tube  and 
add  2  c.c.  filtered  saliva.  Keep  the  tube  several 
hours  at  a  temperature  of  35-40°  C 

The  fibrin  will  not  change. 

Place  0.5  c.c.  neutral  olive  oil  (page  207)  and  2 
c.c.  filtered  saliva  in  a  test-tube. 

Noteworthy  changes  will  be  absent. 

From  these  experiments  it  is  evident  that 
diastase  decomposes  starches,  but  does  not  de- 
compose proteids  and  fats.  Its  ferment  action  is 
thus  far  "  specific."  The  belief  that  each  ferment 
has  its  own  characteristic  product  will  be  in- 
creased by  the  study  of  the  following  typical 
ferment  actions. 

Proteid  Digestion  by  Pepsin 

Gastric  Digestion  of  Cooked  Beef  and  Bread.  — 

At  7  a.m.  feed  cooked  beef  and  bread  to  a  cat 
which  has  fasted  twelve  hours.  At  11  a.  m.  kill 
the  cat,  expose  the  stomach,  and  apply  double 
ligatures  about  1  cm.  apart  to  the  duodenum  at 
the  pylorus  and  to  the  oesophagus  at  the  cardiac 
orifice.  Ptemove  the  stomach.  Open  the  stomach 
very  cautiously  by  drawing  a  knife  along  the 
greater  curvature. 

"  The  stomach  is  very  full,  and  still  contains 


FERMENTATION  193 

much  meat  and  bread  not  wholly  softened.  The 
softening  is  greater  in  the  portal  region  and  in 
those  portions  of  the  food  next  the  mucous  mem- 
brane than  in  the  middle  of  the  stomach  contents. 
The  mucus  secreted  by  the  gastric  mucous 
membrane  is  very  abundant  and  is  strongly  acid. 
The  stomach  contents  have  a  sour  odor."  1 

Artificial  Gastric  Juice.2  —  1.  Strip  the  mucous 
membrane  from  the  fourth  stomach  of  a  calf. 
Wash  the  membrane  with  cold  water  until  the 
acid  reaction  disappears.  Dry  the  mucous  mem- 
brane in  the  air.  Divide  some  of  the  dried 
membrane  into  small  pieces  and  add  dilute  hy- 
drochloric acid.3 

2.  Strip  the  mucous  membrane  of  the  pig  or 
rabbit  from  the  deeper  layers  of  the  stomach,  cut 
the  mucous  membrane  into  the  smallest  pieces, 
wash  slightly  with  water,  pour  off  the  water  with 
all  possible  care,  and  cover  the  slightly  moist 
residue  with  glycerine.4  Before  using,  add  dilute 
hydrochloric  acid. 

1  Eberle  :  Physiologie  der  Verdauung,  1834,  p.  100. 

2  Eberle  :  loc.  cit.,  p.  79. 

3  Dilute  hydrochloric  acid.  —  Add  to  10  c.c.  officinal  HC1, 
sp.  gr.  1.124  (about  25  per  cent  HC1),  enough  water  to  make 
1000  c.c.  This  solution  will  contain  about  0.281  per  cent  HOT. 
(Salkowski's  Practicum,  1893,  p.  130.) 

4  Von  Wittich  :  Archiv  fur  die  gesaramte  Physiologie>  1869, 
ii,  p.  194. 

13 


194  THE    INCOME    OF   ENERGY 

Digestion  with  Artificial  Gastric  Juice.  —  Pre- 
pare three  flasks,  A,  B,  and  C.  In  A  place  100  c.c. 
artificial  gastric  juice;  in  B,  100  c.c.  0.2  per  cent 
HC1;  and  in  C,  a  piece  of  dried  gastric  membrane 
and  100  c.c.  distilled  water.  In  each  of  the  three 
flasks  place  a  small  piece  of  cooked  meat,  and  keep 
the  flasks  about  five  hours  at  35-40°  C.1  Com- 
pare the  result  with  that  observed  in  natural 
digestion. 

The  artificial  gastric  juice  will  digest  the  meat 
as  did  the  natural  juice  in  the  stomach,  but  neither 
the  acid  alone,  nor  the  mucous  membrane  free 
from  acid,  will  digest.  There  is  a  ferment  in  the 
mucous  membrane,  but  it  will  not  act  except  in 
an  acid  medium. 

Extraction  of  Pepsin.  —  Pepsin  more  or  less  con- 
taminated with  proteid  (pepsin  may  itself  be  a  proteid) 
may  be  precipitated  from  a  glycerine  extract  by  alco- 
hol.2 The  pepsin  may  also  be  carried  down  mechani- 
cally by  an  indifferent  precipitate  as  in  Brucke's 
method,3  in  which  the  mucous  membrane,  acidulated 
with  phosphoric  acid,  is  allowed  to  digest  until  the 
proteids  are  mostly  converted  into  soluble  peptone. 
The  mixture  is  then  neutralized  with  lime  water. 
The  insoluble  calcium  phosphate  thus  formed  falls  as 

1  Eberle  :  loc.  cit. 

2  Von  Wittich:  loc.  cit.,  p.  195. 

3  Briicke  :  Sitzungsberichte  der  konigliche  Akadeniie  cler 
Wissenschaften  zu  Wien,  1862,  xliii,  p.  601. 


FERMENTATION  195 

a  fine  powder  carrying  the  pepsin  with  it.  The  precip- 
itate is  dissolved  in  very  dilute  hydrochloric  acid,  and 
to  this  solution  is  added  a  solution  of  cholesterin  in 
alcohol  and  ether.  When  the  two  solutions  are  mixed, 
the  cholesterin  separates  as  an  abundant,  fine  powder 
bearing  the  pepsin  with  it.  The  cholesterin  is  removed 
with  ether,  leaving  the  pepsin. 

Ammonium  sulphate  may  also  be  used  as  the  me- 
chanical precipitant.1 

Change  of  Proteid  to  Peptone    by  Pepsin.  —  1. 

Place  in  a  test-tube  five  drops  of  the  glycerine 
extract  of  pepsin  with  5  c.c.  0.2  per  cent  hydro- 
chloric acid  and  a  small  piece  of  fibrin.2  Keep 
the  mixture  at  35-40°  C. 

In  a  short  time  the  fibrin  will  be  dissolved. 
Appropriate  tests  will  show  that  it  has  been  con- 
verted to  peptone.  2.  Repeat  the  preceding  ex- 
periment, using  commercial  pepsin  (never  very 
free  from  proteid). 

Splitting  of  Casein  by  Eennin. 

Rennin  Extract.  —  Allow  the  mucous  membrane 
of  the  stomach  (preferably  the  fourth  stomach  of 

1  Kiihne  and  Chittenden:  Zeitschrift  fur  Biologie,  1886, 
xxii,  p.  428. 

2  Preparation  of  fibrin.  —  With  a  bundle  of  smooth  rods 
whip  blood  as  it  flows  from  an  artery  until  the  fibrin  gathers  on 
the  rods.  Wash  the  fibrin  in  running  water  until  the  red  cor- 
puscles are  removed  and  the  fibrin  shows  its  natural  color. 
Preserve  the  fibrin  in  glycerine. 


196  THE    INCOME    OF   ENERGY 

the  suckling  calf)  to  stand  twenty-four  hours  in 
150-200  c.c.  0.1-0.2  per  cent  solution  of  hydrochlo- 
ric acid.    Then  neutralize  the  acid  with  great  care.1 

Separation  of  Rennin.  —  The  extract  just  prepared 
contains  pepsin  as  well  as  rennin.  The  rennin  may 
be  separated  as  follows.  The  neutralized  extract  is 
repeatedly  shaken  with  fresh  amounts  of  magnesium 
carbonate.  The  resulting  precipitates  carry  down 
almost  all  the  pepsin  and  very  little  rennin.  The 
filtrate  still  rapidly  coagulates  milk,  but  contains  only 
traces  of  pepsin.  This  filtrate  is  now  precipitated 
with  lead  acetate,  the  precipitate  is  decomposed  with 
very  dilute  sulphuric  acid,  and  the  mixture  filtered. 
To  the  filtrate,  which  contains  the  rennin,  is  added  a 
solution  of  stearin  soap  in  water.  Thereupon  the 
soap  is  thrown  out  of  solution  and  falls,  carrying  the 
rennin  with  it.  The  soap  is  then  removed  by  shaking 
with  ether,  and  the  rennin  remains.2 

Precipitation  of  Casein.  —  Add  1  C.C.  of  the 
neutral  extract  to  25  c.c.  fresh  milk  at  36-38°  C. 
(Normal  milk  is  amphoteric.  If  the  reaction 
be  acid,  the  acid  should  be  very  carefully 
neutralized.) 

In  a  few  minutes  the  milk  will  separate  into 

1  Hammarsten  :  Upsala  Lakareforenings  Fbrhandlingar,  1872, 
viii,  pp.  63-86.  Abstract  by  author  in  Maly's  Jahresbericht 
uber  die  Fortschritte  der  Thierchemie,  1872,  ii,  pp.  118-125. 

2  Hammarsten  :  Lehrbuch  der  physiologischen  Chemie,  1895, 
p.  241. 


FERMENTATION 


197 


curd  and  whey.  The  curd  is  casein  together 
with  the  fat  globules  carried  down  as  it  precipi- 
tates. The  whey  is  a  dilute  saline  solution  of 
milk-albumin,  milk  sugar,  etc. 

Test  the  chemical  reaction.  The  mixture  is 
still  neutral.  Milk  may  also  be  curdled  by  acid, 
either  added  artificially  or  produced  in  the  milk 
itself  by  lactic  acid  fermentation  of  milk  sugar. 
The  absence  of  an  acid  reaction  in  the  above  exper- 
iment excludes  precipitation  through  acid  fermen- 
tation of  milk  sugar.  Casein  prepared  free  from 
milk  sugar  is  also  precipitated  by  rennin.  Finally, 
rennin,  extracted  by  the  method  given  above,  does 
not  act  upon  milk  sugar,  but  rapidly  precipitates 
casein. 

Analogy  suggests  that  the  specific  action  of 
the  rennin  may  be  the  splitting  of  casein  and  that 
the  precipitation  may  be  a  secondary  process. 
The  following  experiments  determine  this  matter. 

Experiments  of  Arthus  and  Pages.1  —  Prepare 
two  solutions,  A  and  B. 


A. 
Milk  100  c.c. 

Neutral  oxalate  of 

potassium  1  %  5  c.c. 

Rennin  1  to  250        4  c.c. 


B. 
Milk  100  c.c. 

Neutral  oxalate  of 

potassium  1  %         5  c.c. 
Water  4  c.c. 


1  Arthus  and  Pages  :  Archives  de  physiologie,  1890,  p.  334. 


198  THE  INCOME   OF   ENERGY 

(Kennin,  1  to  250,  is  a  pastille  of  Hansen  dis- 
solved in  250  c.c.  H20.) 

Keep  both  mixtures  at  38°  C.  during  forty 
minutes.  1.  Boil  25  c.c.  from  each  solution. 
Solution  A  coagulates,  while  solution  B  shows 
no  trace  of  coagulation.  Hence  the  action  of 
rennin  has  rendered  the  casein  in  A  coagulable 
on  boiling. 

2.  To  25  c.c.  from  each  solution  add  8  c.c.  of 
a  solution  of  calcium  chloride  capable  of  pre- 
cipitating exactly,  in  equal  volumes,  the  solution 
of  potassium  oxalate.  By  this  addition  any  ex- 
cess of  potassium  oxalate  is  removed  and  the 
calcium  chloride  remains  in  slight  excess. 

A  will  coagulate ;  B  will  not.  Hence  the  casein 
in  solution  A  has  been  so  changed  by  rennin  that 
it  is  precipitated  on  the  addition  of  a  small  quan- 
tity of  calcium  chloride.  Solution  A  may  also 
be  precipitated  by  restoring  its  original  content 
of  calcium  chloride,  i.e.  by  adding  5  c.c.  of  the 
above  calcium  chloride  solution,  which  will  exactly 
combine  with  the  5  c.c.  of  potassium  oxalate. 

If  small  quantities  of  rennin  be  added  to 
natural  milk  and  equal  portions  of  the  milk  be 
tested  from  time  to  time  by  boiling,  the  amount 
coagulated  will  be  greater  the  longer  the  rennin 
acts.  An  amount  of  calcium  chloride  too  small 
to    produce    coagulation    in    the   early  stages  of 


FERMENTATION  199 

rennin  action  is  sufficient  to  produce  coagulation 
when  added  in  the  later  stages. 

Evidently,  in  the  clotting  of  milk  by  rennin 
two  separate  phenomena  must  be  distinguished: 
(1)  the  chemical  transformation  of  casein  by 
rennin,  (2)  the  precipitation  of  the  transformed 
casein  by  the  calcium  chloride.  (This  salt  favors 
also  the  splitting  of  the  casein.)  Eennin  may 
therefore  be  classed  with  pepsin  and  trypsin. 

According  to  Hammarsten  the  casein  is  split 
into  phosphorus-free  albumose  and  phosphorus- 
holding  paracasein.  Heat  is  set  free.  It  is  the 
paracasein  which  precipitates.  It  is  less  soluble 
than  casein. 

Precipitation  of  Fibrin  by  Fibrin  Ferment 

Buchanan's  Experiment.  —  Press  blood  clot 
through  a  linen  cloth.  Add  the  liquid  thus  ob- 
tained to  a  serous  fluid,  which  does  not  clot  spon- 
taneously, such  as  ascitic  fluid,  pleural  effusion, 
hydrocele  fluid. 

After  some  hours  a  firm,  translucent  clot  will 
form.1 

Extraction  of  Fibrin  Ferment.  Schmidt's  Method. 
—  Coagulate  one  part  of  serum  from  the  blood 

1  Buchanan:  London  Medical  Gazette,  1835,  xviii,  p.  51; 
idem,  1845,  xxxvi,  p.  617.  This  discovery  was  first  announced 
in  1831. 


200  THE   INCOME    OF   ENERGY 

of  ox,  dog,  or  horse,  by  adding  15-20  parts  strong 
alcohol.  After  at  least  fourteen  days,  filter,  dry 
the  moist  residue  over  sulphuric  acid,  pulverize 
the  dried  substance,  stir  it  with  water  (twice  the 
volume  of  the  serum  originally  taken)  and  after 
allowing  sufficient  time  for  solution,  filter.  The 
filtrate  contains  the  fibrin  ferment.1 

Gamgee's  Method.  —  Allow  freshly  prepared  fi- 
brin (obtained  by  washing  a  blood  clot  free  from 
corpuscles)  to  stand  three  days  in  8.0  per  cent 
solution  of  sodium  chloride.     Filter.2 

The  filtrate  is  rich  in  fibrin  ferment. 

Extraction  of  Fibrinogen.  —  Eeceive  three 
volumes  of  blood  directly  from  an  artery  into 
one  volume  of  saturated  solution  of  magnesium 
sulphate,  which  will  prevent  the  blood  from 
clotting.  Separate  the  corpuscles  from  the  liquid 
plasma  by  the  centrifugal  machine.  Add  to  the 
plasma  an  equal  volume  of  saturated  solution  of 
sodium  chloride.  Flakes  of  fibrinogen  will  be 
precipitated.  Filter  as  quickly  as  possible,  for 
that  purpose  dividing  the  liquid  among  several 
funnels  each  with  a  folded  filter  paper.  Press 
the  filter  papers  containing  the  residue  between 
fresh  filter  paper,  in  order  to  remove  the  adherent 

1  Schmidt :  Archiv  fiir  die  gesammte  Thysiologie,  1872,  vi, 
p.  457. 

2  Gamgee  :  Journal  of  physiology,  1879,  ii,  p.  151. 


FERMENTATION  201 

liquid.  Tear  the  filter  containing  the  fibrinogen 
into  small  pieces.  Dissolve  the  fibrinogen  which 
sticks  to  the  filter  as  a  tough,  elastic  mass,  in  a 
quantity  of  8  per  cent  sodium  chloride  solu- 
tion equal  to  about  one-third  the  quantity  of  the 
magnesium  sulphate  solution  originally  taken. 
Filter  off  the  fragments  of  paper.  Purify  by 
reprecipitation  with  an  equal  volume  of  saturated 
solution  of  sodium  chloride.  Filter.  Dry  as 
before,  and  add  a  small  quantity  of  water  to  the 
finely  divided  filter  to  which  the  precipitate 
clings.  This  water  will  take  a  small  quantity  of 
salt  from  the  precipitate,  and  in  this  dilute  saline 
solution  the  fibrinogen  will  dissolve.1 

Precipitation  of  Fibrinogen  by  Fibrin  Ferment. — 
Add  to  the  dilute  saline  solution  of  fibrinogen  a 
solution  containing  fibrin  ferment. 

Fibrin  will  gradually  form. 

Ammoniacal  Fermentation  of  Urea  by 
Urease 

1.  Place  100  c.c.  fresh  human  urine  in  each 
of  three  clean  flasks  marked  A,  B,  C.  To  B  and 
C  add  1  c.c.  of  urine  that  has  become  ammoniacal 
upon  standing  in  the  atmospheric  air.     Add  also 

1  Hammarsten  :  Archiv  fiir  die  gesammte  Physiologie,  1879, 
xix,  p.  563.  Also  idem,  1880,  xxii,  p.  431.  Hammarsten's  first 
publication  was  in  Nova  acta  regia  societas  scientiarum  Upsali- 
ensis,  1878,  (3),  ix. 


202         THE  INCOME  OF  ENERGY 

to  G  2  per  cent  of  a  saturated  solution  of  carbolic 
acid  in  water.  Let  B  and  G  stand  in  a  warm 
place  sixteen  days. 

2.  Withdraw  5  c.c.  from  flask  A.  Note 
whether  the  urine  is  clear  or  turbid,  and 
whether  it  effervesces  on  the  addition  of  a 
dilute  acid.  Withdraw  2  c.c.  from  flask  A  and 
determine  its  percentage  of  urea  by  the  hypo- 
bromite  method. 

Centrifugalize  a  portion  of  the  remaining  con- 
tents of  flask  A.  With  a  microscope  examine 
the  sediment  for  crystals  of  ammonio-magnesium 
phosphate  and  for  micro-organisms,  especially  the 
micrococcus  ureas,  which  occurs  in  long  curved 
chains  of  round  cells  about  1.5  /jl  in  diameter. 

3.  After  sixteen  days  repeat  these  observa- 
tions on  the  urine  in  flasks  B  and  G.  Eecord 
the  results  obtained  from  all  three  flasks  in  the 
table  on  page  203. 

The  table  shows  that  the  hydrolysis  of  urea 
into  ammonium  carbonate  still  takes  place  in 
urine  containing  enough  carbolic  acid  to  destroy 
the  micro-organisms  long  known  to  be  the  cause 
of  the  ammoniacal  fermentation.1  It  is  therefore 
probably  due  to  a  ferment,  which  escapes  from 
the  cells  after  their  death. 

1  Hoppe-Seyler :  Medicinisch-chemische  Untersuchungen, 
Berlin,  1866,  p.  570. 


FERMENTATION 


203 


GO 

"  to 
O 

Crystals  of 
Ammonio- 
Magnesium 
Phosphate. 

Per  cent 

of 

Urea. 

Reaction 

to 

Acids. 

Clear 

or 

Turbid. 

• 

Content 

of 

Carbolic 

Acid. 

CO 

A 

Normal 

B 

Septic 

C 
Aseptic 

204  THE    INCOME   OF   ENERGY 

Prior  to  1860  ammoniacal  decomposition  of 
urine  was  vaguely  classed  as  a  fermentation.  In 
that  year  Miiller1  suggested  that  it  might  be  due 
to  a  body  like  beer-yeast.  In  1862  Pasteur2 
discovered  such  a  yeast,  which  he  called  Torula 
urece.  Cohn  first  classed  it  with  the  micrococci. 
It  is  aerobic.  Miguel  finds  seven  species  of 
bacilli,  nine  micrococci,  and  one  sarcina,  that 
decompose  urea.  These  obtain  their  nitrogen 
ordinarily  from  proteids,  but  in  the  absence  of 
proteids  may  utilize  urea. 

Extraction  of  Urease.  —  To  10  C.C.  of  urine 
undergoing  an  active  ammoniacal  fermentation, 
add  50  c.c.  of  strong  alcohol,  and  allow  the 
mixture  to  stand  in  a  well-corked  flask.  After 
five  days  place  the  precipitate  upon  a  very  small 
filter  and  wash  it  with  50  c.c.  of  fresh  alcohol. 
(Preserve  both  filtrates  for  recovery  of  the  alcohol 
by  redistillation.) 

1.  Add  a  very  small  quantity  of  this  precip- 
itate to  a  neutral  2  per  cent  solution  of  urea. 
Test  the  reaction.  Place  the  mixture  in  a  water 
bath  at  38°  C. 

After  a  few  minutes  again  test  the  reaction. 

It  will  be  strongly  alkaline. 

1  Miiller:  Journal  fur  praktische  Chemie,  1860,  lxxxi,  p.  467. 

2  Pasteur  :  Comptes  rendus  de  l'academie  des  sciences,  Paris, 
1860,  1,  p.  869.     See  also  Van  Tieghem,  idem,  1864,  p.  210. 


FERMENTATION  205 

After  a  short  time  the  odor  of  ammonia  will  be 
perceptible.  The  alcoholic  precipitate  contains  a 
ferment  capable  of  quickly  hydrating  urea. 

"The  alcoholic  precipitate  from  the  unfiltered 
urine  consists  chiefly  of  various  salts  together 
with  the  cells  of  the  Torula,  hence  when  treated 
with  water  some  of  the  salts  are  dissolved  and 
pass  with  the  ferment  through  the  filter.  If  this 
first  aqueous  extract  be  again  precipitated  with 
alcohol,  a  portion  of  the  salts  will  be  again 
removed,  and  if  this  second  precipitate  be  several 
times  redissolved  in  water  and  reprecipitated 
with  alcohol,  the  body  with  the  ferment  proper- 
ties may  be  ultimately  separated  —  as  an  amor- 
phous white  powder  soluble  to  a  clear  solution 
in  distilled  water  and  not  characterized  by  any 
special  chemical  reactions." 

The  ferment  is  not  secreted  by  the  cells  into 
the  surrounding  liquid,  but  is  retained  within  the 
cell  bodies,  for  the  living  cells  may  be  filtered  off, 
and  the  filtrate  will  not  hydrate  the  urea.1 

Splitting  and  Synthesis  of  Fats 

Chemistry  of  Fats  and  Soaps.  —  When  olive  oil 
is  saponified,  glycerine   appears  (Scheele,  1779). 

1  Lea  :  Journal  of  Physiology7,  1885,  vi,  p.  138.  See  also 
Musculus :  Comptes  reudus  de  l'academie  des  sciences,  Paris, 
1874,  lxxviii,  p.  132  ;  idem,  1876,  lxxxii,  p.  333  ;  Archiv  fur 
die  gesammte  Physiologie,  1876,  xii,  p.  214. 


206         THE  INCOME  OF  ENERGY 

It  is  related  to  the  alcohols  (Chevreul,  1813), 
being  a  compound  ether  or  ester,  a  combination 
of  an  alcohol  with  an  acid.  Commercially  gly- 
cerine is  prepared  by  exposing  neutral  fats,  such 
as  stearin,  to  superheated  steam,  whereby  the 
neutral  fat  is  split  into  glycerine  and  fatty  acid. 


CH20 

•CO(CH2)16 

CH3 

H 

OH 

CHO 

•  CO(CH2)16 

•CH3 

+ 

H 

OH 

= 

CH20 

'CO(CH2)16 

CH3 

H 

•OH 

STEARIN 

WATER 

CH2 

•OH 

CO 

1 

•OH(CH2)16-CH3 

CH 

•OH 

+ 

1 
CO 

1 

•OH(CH2)16-CH3 

CH2 

•OH 

1 
CO 

•OH(CH2)16'CH3 

GLYCERINE 

STEARIC   ACID 

If  an  alkali  be  present,  it  will  combine  with 
the  fatty  acid  to  form  a  soap. 

CO-OH(CH2)16-CH3 
CO'OH(CH2)16-CH8 
CO-OH(CH2)16-CH3 

STEARIC    ACID 


Na-OH 

+         Na  •  OH        = 

Na-OH 

SODIUM 

HYDROXIDE 

CO  •  ONa(CH2)16  •  CH3 

HOH 

GO-ONa(CH2)16-CH8 

+ 

HOH 

CO-ONa(CH2)16.CH3 

H-OH 

SODIUM    STEARATE 

WATER 

Splitting  of  Fats  by  the  Pancreatic  Juice.      Ber- 
nard's Experiment.  —  Place   2  c.c.  neutral  olive 


FERMENTATION  207 

oil  in  a  test-tube  and  add  a  small  quantity  of 
pancreatic  juice  (or  a  piece  of  fresh  pancreas  or 
extract  of  pancreas).  Test  the  reaction  of  the 
mixture.  It  is  alkaline.  Note  that  a  white, 
creamy  liquid  forms  almost  immediately.  This 
"  emulsion  "  is  composed  of  a  multitude  of  small 
fat  globules. 

Test  the  reaction  again.  It  gradually  becomes 
acid. 

It  is  evident  that  under  the  influence  of  the 
pancreatic  juice  the  fatty  matter  is  not  simply 
finely  divided  and  emulsified,  but  that  it  has  also 
been  modified  chemically.1 

In  order  to  study  the  splitting  of  neutral  fats 
by  lipase,  a  ferment  found  in  the  pancreatic  juice, 
it  is  necessary  (1)  to  prepare  a  perfectly  neutral 
fat,  and  (2)  to  recognize  the  fatty  acid  as  soon  as 
it  is  set  free. 

Preparation  of  Neutral  Fat.  —  Shake  commer- 
cial olive  oil  (which  always  contains  fatty  acid) 
for  two  hours  at  95°  C.  in  a  separating  funnel 
with  a  saturated  solution  of  barium  hydroxide. 
Allow  the  mixture  to  stand  until  the  oil  sepa- 
rates from  the  hydroxide.  Kemove  the  hydrox- 
ide.    Filter  the  oil. 

The    Emulsion    Test   for   Fatty   Acid.      Briicke's 

1  Bernard  :  Comptes  rendus  de  l'academie  des  sciences,  Paris, 
1849,  xxviii,  p.  250. 


208         THE  INCOME  OF  ENERGY 

Experiment.  —  1.  Shake  1  c.c.  neutral  olive  oil 
in  a  test-tube  with  5  c.c.  0.25  per  cent  sodium 
carbonate  solution. 

The  oil  will  be  broken  up  into  large  globules 
which  will  speedily  reunite,  leaving  the  liquid 
clear. 

2.  Shake  1  c.c.  rancid  olive  oil  (containing 
about  5.5  per  cent  fatty  acid)  with  5  c.c.  0.25  per 
cent  sodium  carbonate  solution. 

The  mixture  becomes  instantly  milky.  The 
oil  is  divided  into  globules  of  microscopic  size. 
The  emulsion  is  permanent. 

3.  Shake  1  c.c.  neutral  olive  oil  with  5  c.c.  water. 
The  water  and  oil  will  not  mix. 

4.  Shake  1  c.c.  neutral  oil  with  water  con- 
taining soap. 

The  oil  will  be  emulsified.  It  is  probable 
therefore  that  soap  contributes  to  the  emulsion, 
perhaps  by  coating  the  fine  particles  of  oil  with  a 
membrane  that  prevents  their  reunion.1 

Gad's  Experiment.  —  1 .  Fill  a  watch  glass 
about  5  cm.  in  diameter  with  0.25  per  cent  solu- 
tion of  sodium  carbonate.  With  a  glass  rod 
carefully  place  a  large  drop  of  rancid  olive  oil 
(containing  5.5  per  cent  fatty  acid)  upon  the 
surface  of  the  soda  solution. 

1  Briioke :  Sitzungsberichte  der  kaiserlichen  Akadeniie  der 
Wissenschaften  zu  Wien,  1870,  lxi,  pp.  613-614. 


FERMENTATION  209 

The  drop  will  come  to  rest,  and  for  a  moment 
both  the  drop  and  the  surrounding  liquid  remain 
clear.  Very  soon,  however,  the  oil  is  covered 
with  a  white  layer,  and  through  the  soda  solu- 
tion spreads  a  white  cloud  which  becomes  denser 
and  denser  until  the  oil  drop,  steadily  diminish- 
ing in  size,  floats  in  a  milky  white  liquid. 

2.  Eepeat  the  experiment,  observing  the  oil 
drop  under  a  low  power  of  the  microscope. 

Note  the  extraordinary  motion  in  the  neigh- 
borhood of  the  oil  drop,  and  how  the  particles  of 
oil  are  thrown  out  in  strong  eddies. 

3.  Examine  the  completed  emulsion  under  a 
higher  power  of  the  microscope. 

There  appear  exceedingly  small  fat  drops  of 
very  uniform  size.  The  milky  fluid  is  the  finest 
and  most  uniform  emulsion.1 

RachforcV s  Experiment.  —  "  Arrange  a  series  of 
watch  glasses  containing  0.25  per  cent  solution 
sodium  carbonate.  Place  in  a  test-tube  2  c.c. 
neutral  olive  oil  and  1  c.c.  pancreatic  juice  (or 
extract).  Shake  the  tube  and  allow  the  juice 
and  oil  to  separate,  then  pipette  a  drop  of  oil 
from  the  surface  and  place  it  on  the  soda  solu- 
tion-in  watch  glass  1.  Again  shake  the  tube 
and  allow  the  oil  and  juice  to  separate,  then 
pipette  as  before,  placing  a  drop  of  oil  in  watch 

1  Gad:  Archiv  fur  Physiologie,  1878,  p.  183. 
14 


210  THE   INCOME    OF    ENERGY 

glass  2.  Again  shake  and  pipette  as  before,  and 
repeat  this  process  every  three  or  four  minutes 
until  the  experiment  is  completed.  The  begin- 
ning of  the  experiment  and  the  time  of  each 
pipetting  must  be  carefully  noted.  If  the  pipet- 
tings  are  three  minutes  apart,  then  the  first  drop 
of  oil  will  have  been  exposed  three  minutes  to 
the  action  of  the  pancreatic  juice,  the  second 
drop  six  minutes,  the  third  nine  minutes,  and 
so  on.1 

The  gradual  increase  in  fatty  acid  will  be 
shown  by  the  gradual  increase  in  the  amount 
of  the  spontaneous  emulsion.2 

It  has  just  been  shown  that  lipase  will  hydro- 
lyze  neutral  fats  into  fatty  acid  and  glycerine. 
We  must  now  enquire  whether  this  ferment 
ean  effect  the  synthesis  of  fats,  in  other  words 
whether  its  action  is  reversible.     For  this  pur- 

1  Raehford:  Journal  of  physiology,  1891,  xii,  p.  81.  Rach- 
ford  used  J  c.c.  fresh  pancreatic  juice  obtained  by  placing  a 
glass  tube  in  the  pancreatic  duct  of  the  rabbit  (see  page  80). 

2  "  There  is  a  possible  error  in  this  method  which  had  better 
be  spoken  of  here.  It  would  seem  that  the  alkali  of  the  pan- 
creatic juice  would  combine  with  the  fatty  acids  forming  soap, 
and  in  this  way  the  oil  would  soon  be  emulsified  in  the  juice 
itself  and  not  separate  after  shaking.  This  would  indeed  be  a 
serious  drawback  if  it  actually  occurred,  but  in  truth  it  does  not 
occur  until  late  in  the  experiment  after  we  have  obtained  the 
information  we  have  sought  by  the  spontaneous  emulsion 
method."     (Raehford,  loc.  cit.,  p.  82). 


FERMENTATION  211 

pose  an  extract  of  lipase  may  be  used,  first,  to 
split  a  neutral  fat  (or  glycerol  ester)  into  its  con- 
stituent fatty  acid  and  alcohol  (glycerine  is  a 
trihydric  alcohol),  and  second,  to  form  a  neutral 
fat  from  fatty  acid  and  alcohol. 

Extraction  of  Lipase.  .  From  Pancreas.  —  Ee- 
move  the  pancreas  of  the  pig  within  thirty  min- 
utes after  the  death  of  the  animal.  Dissect  off 
as  much  of  the  fat  as  possible.  Eeduce  the  pan- 
creas to  a  fine  pulp  in  a  mortar  with  coarse  well- 
washed  white  sand.  Extract  the  lipase  with  a 
little  water  or  glycerine. 

From  Liver.  —  Eemove  the  liver  of  the  pig 
within  thirty  minutes  of  the  death  of  the  animal. 
Eeduce  50  gms.  to  a  fine  pulp  in  a  mortar  with 
about  200  c.c.  water.  Filter.  Dilute  the  watery 
extract  to  500  c.c. 

Hydrolysis  of  Ethyl  Butyrate  by  Lipase.  — 
Place  in  each  of  two  test-tubes,  A  and  B,  4  c.c. 
water,  0.1  c.c.  toluene,1  and  0.26  c.c.  ethyl  buty- 
rate.2 Cork  the  tubes  tightly.  Place  them  in  the 
water  bath  for  five  minutes,  to  bring  them  to 
the  temperature  of  the  bath,  40°  C.     Add  1  c.c.  of 

1  Toluene  is  an  antiseptic,  which  prevents  the  splitting  of 
the  neutral  fat  by  bacteria. 

2  Ethyl  butyrate  hydrolyzes  more  rapidly  than  butter  fat. 
It  has  the  further  advantage  that  the  amount  split  by  the 
temperatures  employed  during  the  time  of  the  experiment  is  too 
small  to  be  measurable. 


212         THE  INCOME  OF  ENERGY 

the  aqueous  extract  of  lipase  to  each.  Boil  tube 
B.  Place  both  tubes  at  40°  C.  for  fifteen  min- 
utes. Eemove  them  from  the  bath  and  plunge 
them  into  ice-water  (to  check  further  ferment 
action).  Titrate  with  ^  KOH,  using  neutral  lit- 
mus as  the  indicator.1     The  initial  acidity  of  the 

1  A  normal  solution  contains  in  each  litre  one  equivalent 
weight  of  the  active  substance,  i.  e.  that  mass  of  the  active  sub. 
stance  which  is  equivalent  to  the  atomic  weight  of  a  univalent 
element  in  the  reaction  for  which  the  normal  solution  is  to  be 
employed.  Equal  volumes  of  different  normal  solutions  are 
equivalent  to  each  other.  Thus,  1  c.c.  normal  alkali  solution 
requires  for  neutralization  exactly  1  c.c.  normal  acid,  no  matter 
what  acid  is  employed  to  make  the  normal  solution. 

Preparation  of  Normal  Potassium  Solution.  —  The  content  of 
KOH  in  1  litre  is  56.16  grams.  Dissolve  60  gms.  purest  com- 
mercial KOH  (which  always  contains  considerable  water)  in  a 
graduated  cylinder  in  about  950  c.c.  water.  Determine  the 
true  content  of  KOH  by  titration  with  a  normal  oxalic  acid 
solution  (prepared  by  dissolving  its  equivalent  weight  63  gms. 
in  1  litre  water)  as  follows.  Thoroughly  stir  the  potassium  hy- 
droxide solution,  fill  a  burette  with  a  portion  of  the  well-mixed 
solution.  Place  10  c.c.  normal  oxalic  acid  solution  in  a  beaker 
and  add  a  few  drops  of  solution  of  rosolic  acid  as  indicator. 
Add  the  alkali  from  the  burette  cautiously  until  the  end  point 
of  the  reaction  is  reached,  i.  e.  until  the  indicator  gives  a  red 
color  which  does  not  quickly  disappear.  As  10  c.c.  of  acid  solu- 
tion should  exactly  neutralize  10  c.c.  of  alkali  solution,  pro- 
vided both  were  normal,  it  follows  that  the  quantity  of  KOH 
solution  necessary  to  neutralize  is  to  10  c.c.  as  the  total  quantity 
of  the  original  KOH  solution  is  to  x.  x  will  be  the  number  of 
cubic  centimetres  to  which  the  KOH  solution  must  be  diluted 
in  order  to  make  it  normal.  A  portion  of  the  normal  solution 
should  then  be  diluted    1:20,   and   preserved    in  an  air-tight 


FERMENTATION  213 

enzyme  solution,  usually  0.1  to  0.2  c.c.  ^V  KOH, 
should  be  deducted  from  the  cubic  centimetres 
KOH  required  to  neutralize  the  fatty  acid 
formed.1 

Fatty  acid  will  appear  in  tube  A,  but  not  in 
tube  B,  in  which  the  enzyme  was  destroyed  by 
boiling. 

Synthesis  of  Neutral  Fat  by  Lipase.  —  1.  Place 
5  c.c.  t^-q  butyric  acid,  2  c.c.  13  per  cent  alcohol, 
1  c.c.  diluted  glycerine  extract  of  pig's  pancreas 
(or  aqueous  extract  of  liver)  in  each  of  two  test- 
tubes,  A  and  B.  Boil  the  contents  of  test-tube 
B.  Seal  both  tubes.  Keep  them  thirty-six 
hours  at  48.5°  C. 

On  opening  the  tubes,  A  will  give  a  distinct 
odor  of  ethyl  butyrate ;  none  will  be  found  in  B, 
in  which  the  ferment  was  destroyed  by  boiling.2 

2.  Place  5  gms.  glycerine,  2  gms.  isobutyric 
acid,  125  gms.  water,  1  c.c.  neutralized  blood  serum 
(or  aqueous  extract  of  pig's  liver)  in  each  of  two 

flask.     (Compare    Miiller   and  Kiliani :   Kurzes   Lehrbuch   der 
analytischen  Chemie,  1900,  p.  31  and  p.  83). 

At  30°  (summer  temperature)  0.26  c.c.  ethyl  butyrate  weighs 
0.2300  gram.  This  quantity,  if  completely  hydrolyzed,  would 
require  39.7  c.c.  ^  KOH. 

1  Kastle  and  Loeveuhart :  American  chemical  journal,  1900, 
xxiv,  pp.  491-525.  Also  Loevenhart :  American  journal  of 
physiology,  1902,  vi,  pp.  331-350. 

2  Kastle  and  Loevenhart :  loc.  cit.,  p.  518. 


214         THE  INCOME  OF  ENERGY 

test-tubes,  A  and  B.  Boil  the  contents  of  tube 
B.  Place  both  at  37°  C.  At  intervals  of  half 
an  hour  titrate  a  portion  from  each  tube  with 
7tq  KOH  solution.  The  acidity  will  diminish  in 
both,  but  much  more  rapidly  in  the  tube  contain- 
ing the  active  ferment. 

The  acidity  is  diminished  by  the  combination 
of  the  fatty  acid  with  the  glycerine  to  form  a 
neutral  fat.1 

Fats  are  hydrolyzed  to  some  extent  in  the  stomach,2 
but  stomach  lipase  is  active  only  in  neutral  solutions. 
It  is  inhibited  or  destroyed  by  0.3  per  cent  hydro- 
chloric acid.  Other  ethereal  salts  besides  the  fats  are 
hydrolyzed  in  the  intestine,  e.  g.  salol.8 

The  rate  of  change  by  lipase  increases  with  the 
amount  of  the  enzyme  present.4 

Reversible  action  is  seen  in  ferments  other  than 
lipase,  as  in  the  following  experiments. 

Splitting  of  Hippuric  Acid  by  Histozyme.  —  A  pig's 
kidney  was  perfused  four  hours  with  one  litre  defibri- 
nated    pig's    blood   to  which  0.8   gram  hippuric  acid 

1  Hanriot :  Comptes  rendus  de  la  societe  de  biologic,  1901, 
p.  70. 

2  Marcet:  Proceedings  Royal  Society,  London,  1858,  ix. 
p.  306.  Ogata  :  Archiv  fur  Physiologie,  1881,  p.  515.  Cash  : 
Archiv  fur  Physiologie,  1880,  p.  323. 

3  Baas:  Zeitschrift  fur  physiologische  Chemie,  1890,  xiv, 
p.  416. 

4  Kastle  and  Loevenhart :  loc.  cit.,  p.  511. 


FERMENTATION  215 

(sodium  salt)  had  been  added.  The  blood  passed 
through  the  kidney  9-10  times. 

Upon  analysis,  there  appeared  0.087  gram  benzoic 
acid,  produced  from  0.1276  gram  hippuric  acid. 

Synthesis  of  Hippuric  Acid  by  Histozyme.  — A  pig's 
kidney  was  perfused  three  hours  with  one  litre  defibri- 
nated  pig's  blood  containing  a  neutral  solution  of  0.5 
gram  benzoic  acid  and  0.6  gram  glycocoll.  The  blood 
passed  ten  times  through  the  kidney. 

Found  :  94  mgm.  hippuric  acid.1 

These  actions  depend  upon  a  ferment,  histozyme, 
extracted  by  Schmiedeberg. 

Some  hypothetical  considerations  will  be  of  value 
here.  Compounds  of  carbon  may  be  divided  into 
those  in  which  the  carbon  atoms  are  arranged  in  an 
open    chain,  for  example  ethane,  C2H6, 

H   H 

I       I 
H— C— C— H 

I       I 
H   H 

ETHANE 

and  those  in  which  the  chain  is  closed  to  form  a  "  car- 
bon ring,"  for  example,  benzene,  C6H6,  which  consists 
of  six  carbon  atoms,  in  a  closed,  ring-shaped  chain,  the 
"benzene  nucleus,"  with  a  hydrogen  atom  joined 
to  each  carbon  atom  by  its  fourth  affinity  (Kekule, 
1865). 

1  Schmiedeberg :  Arehiv  fur  experiments le  Pathologie  mid 
Pharmakologie,  1881,  xiv,  pp.  382-383. 


216  THE    INCOME    OF   ENERGY 


\ 

/ 

c 

=  c 

/ 

\ 

-c 

c- 

.  % 

// 

c 

-c 

/ 

\ 

BENZENE 

NUCLEUS 

OR 

RING 

H  H 

\  / 

C  =  C 

/  \ 

H-C  C-H 

%         // 

c-c 

/        \ 

H  H 

BENZENE 


The  benzene  ring  is  not  easily  opened,  but  deriva- 
tives of  benzene  may  be  readily  obtained  by  replacing 
hydrogen  atoms.  Thus,  in  aniline  or  amido-benzene, 
C6H5.NH2,  one  hydrogen  atom  is  replaced  by  amide 
radical ;  in  carbolic  acid,  or  phenol,  C6H5.OH,  by 
hydroxyl ;  in  toluene  or  methyl  benzene,  C6H5.CH3, 
by  the  radical  CH3.  The  carbon  atom  in  methyl 
benzene  is  not  a  part  of  the  benzene  ring,  but  is 
chained  to  the  side  of  the  ring.  The  hydrogen  atoms 
in  the  side-chain  differ  in  their  affinities  from  those 
attached  to  the  ring;  the  hydrogen  in  the  ring  may 
be  replaced  by  groups  {e.g.  N02)  which  will  not  readily 
replace  the  hydrogen  of  the  side-chain.  This  is  a 
matter  of  special  interest  in  relation  to  the  specific 
action  of  poisons,  ferments,  etc.  By  substituting 
hydroxyl  for  the  hydrogen  of  the  side-chain,  benzyl 
alcohol,  C6H6.CH2.OH,  is  formed.  By  introducing 
carboxyl,  benzoic  acid,  C6H5.CO.OH,  is  obtained.  It 
has  been  shown  above  that  benzoic  acid  and  glyco- 
coll  are  united  in  the  kidney  to  form  hippuric  acid. 
Glycocoll  is  amido-acetic  acid,  CH2(NH2).CO.OH.     It 


FERMENTATION  217 

unites  with  benzoic  acid  by  replacing  the  hydroxy  1  in 
the  side-chain,  thus  forming 


C6HB.CO.NHx 
CO.OH'' 

HIPPURIC   ACID 


CH2 


Cinnamic  acid,  toluene,  and  other  aromatic  substances 
are  similarly  excreted  as  hippuric  acid  when  taken 
internally. 

The  reversible  action  of  the  kidney  ferment  is  im- 
portant in  hastening  the  establishment  of  the  equi- 
librium between  benzoic  acid  and  glycocoll.  If  these 
two  bodies  pass  through  the  kidney,  a  certain  amount 
of  hippuric  acid  is  formed ;  if  hippuric  acid  itself 
passes  through  the  kidney,  a  certain  quantity  is  hy- 
drolyzed. 

Relation  of  Reversible  Action  to  Absorption  of  Fat. — 
"Pancreatic  juice  is  capable  of  hydrolyzing  all  the  fat 
of  a  fatty  meal  in  the  period  of  pancreatic  digestion. 
In  the  living  intestine  the  hydrolysis  should  be  com- 
plete, inasmuch  as  the  removal  of  the  products  of  the 
hydrolysis  by  absorption  prevents  the  establishment 
of  equilibrium.  On  the  other  hand,  the  products  of 
the  hydrolysis  in  their  transition  through  the  epithelial 
cells  come  in  contact  with  a  lipolytic  enzyme,  the  pres- 
ence of  which  in  these  cells  has  been  demonstrated  in 
the  above. 

"  The  lipase  now  finds  itself  in  contact  with  only 
fatty  acid  and  glycerine,  and  hence  in  acting  catalyti- 
cally  to  bring  about  the  chemical  equilibrium,  it  effects 


218        THE  INCOME  OF  ENERGY 

the  synthesis  of  a  fat.  This  would  offer  a  satisfactory 
explanation  of  the  presence  of  fat  granules  in  these 
cells.  As  the  fatty  acid  and  glycerine  diffuse  out  of 
the  cells  through  the  basement  membrane,  the  fat 
in  these  cells  would  speedily  disappear  were  it  not  that 
these  substances  were  constantly  being  absorbed  from 
the  lumen  of  the  intestine.  When  absorption  ceases, 
however,  the  fat  present  is  at  once  hydro lyzed  by  the 
lipase  present.  This  hydrolysis  is  in  all  probability 
complete  for  the  reason  that  the  products  of  the 
hydrolysis,  viz.,  glycerine  and  fatty  acid,  are  being 
constantly  removed  by  diffusion.  According  to  this 
view,  therefore,  no  fat  ever  enters  or  leaves  the  epi- 
thelial cells  as  such,  but  as  fatty  acid  and  glycerine. 

"  These  two  substances  then  enter  the  central 
lacteal,  where  equilibrium  is  again  established  and 
there  is  a  large  production  of  fat." * 

Immunity 

Ehrlich's  Ricin  Experiments.2  —  Powder  Albert 
biscuits  weighing  6.75  grams.     Add  to  each  cake 

1  Kastle  and  Loevenhart:  loccit.,  p.  522. 

2  Ehrlich  :  Deutsche  medicinische  Wochenschrift,  1891, 
xvii,  pp.  976-979. 

Ricin  is  a  toxalbumin  extracted  from  the  seeds  of  the  castor 
oil  plant.  It  is  poisonous  in  the  slightest  traces.  Weight  for 
weight  it  is  a  billion  timss  more  poisonous  than  corrosive  sub- 
limate. Intravenous  injection  of  0.03  milligram  (0.00003  gram) 
per  kilo  of  body  weight  is  fatal.  One  gram  commercial  ricin 
would  kill  one  and  one-half  million  guinea-pigs.  The  effect  is 
about  one  hundred  times  less  when  taken  by  the  mouth,  yet 


FERMENTATION  219 

3.2-3.5  c.c.  of  water  containing  ricin.  The  be- 
ginning content  of  ricin  should  be  0.02  gm.  ricin 
for  each  cake  ;  0.035  gm.  is  fatal  in  the  course 
of  five  or  six  days.  Mix  the  biscuit  powder  and 
ricin  solution  to  a  stiff  dough,  roll  the  dough  into 
rods,  divide  them  into  equal  lengths,  and  dry 
the  portions  quickly  on  a  wire  sieve.  Determine 
the  effect  on  white  mice  of  successively  increas- 
ing doses,  as  follows : 

DAY  DOSE 


1 

0.002  c 

2 

.  .   . 

3 

0.006 

4 

0.008 

5 

.   .   . 

6 

0.01 

7 

0.0125 

8 

0.015 

DAY 

DOSE 

9 

0.02 

10 

0.03 

11 

0.04 

12 

0.05 

13 

0.06 

14 

•   .  . 

15 

0.08 

16 

0.01 

On  the  17th  day  inject  subcutaneously  a  fresh 
mouse  with  the  fatal  dose  —  1  c.c.  of  a  Ytnfowo  so~ 
lution  per  20  gm.  of  mouse.     At  the  same  time 


even  thus  0.18  gram  will  kill  a  full-grown  man.  The  cause  of 
death  is  agglutination  of  red  blood  corpuscles,  and  hence 
multiple  thrombosis,  especially  of  the  abdominal  vessels. 
Clinically,  violent  diarrhcea  and  progressive  exhaustion  are  ob- 
served. The  toxicity  is  greatly  dependent  on  species.  Guinea- 
pigs  are  far  more  susceptible  than  white  mice.  With  white 
mice  the  fatal  subcutaneous  injection  is  1  c.c.  of  a  solution  con- 
taining ^sWiJ  ricin  per  20  grams  of  body  weight. 


220        THE  INCOME  OF  ENERGY 

inject   the   immunized   mice   with  a    dose    one 
hundred  times  as  great.1 

Observe  the  non-immune  and  the  immune  mice 
for  several  days  and  note  the  results. 

Ehrlich  continued  the  above  experiment  until  the 
immunized  mouse  received  daily  0.5  gm.  of  the  ricin 
by  the  mouth.  Such  animals  bore  safely  subcutaneous 
injections  of  z^q  and  even  more.  The  immunity  also 
appeared  in  that  solutions  of  0.5-1.0  per  cent  applied 
to  the  eyes  of  non-immune  mice  caused  violent  pano- 
phthalmitis, while  immune  mice  bore  easily  the  appli- 
cation of  10  per  cent  solutions. 

This  absolute  local  immunity  was  fully  established 
when  the  general  immunity  had  attained  only  a 
middle  grade.  Normally  the  subcutaneous  injection 
of  ^ooVou  ricm  solution  causes  severe  local  inflamma- 
tion, but  thoroughly  immunized  animals  bear  toVq. 
Quantitative  experiments  show  that  the  resistance  to 
the  poison  is  not  increased  during  the  first  four  days, 
and  the  increase  is  doubtful  on  the  fifth  day,  but  on 
the  sixth  day  a  relatively  high  (for  example  thirteen- 
fold)  general  immunity  is  suddenly  established.  The 
sudden  fall  toward  normal  temperature  observed  in 
diseases  with  a  "crisis,"  such  as  pneumonia,  may  de- 
pend on  the  "  critical  "  establishment  of  immunity. 

Immunity  is  not  increased  by  continued  administra- 
tion of  the  same  dose,  day  by  day.  An  equilibrium 
appears  to  be  established. 

1  The  mice  in  these  experiments  must  be  carefully  protected 
against  cold  and  wetting. 


FERMENTATION  221 

The  immunity  once  established  endures  a  consider- 
able time  ;  six  months  and  possibly  much  longer. 

Ricin  Antitoxine.  —  Defibrinate  the  blood  of  the 
immunized  mice.  Divide  it  into  two  portions. 
1.  To  one  portion  add  ricin  solution  in  such  a 
ratio  that  the  mixture  shall  contain  yo  0V0  o>  *■  e- 
twice  the  fatal  amount. 

Inject  a  fresh  mouse  subcutaneously  with  1  c.c. 
of  this  mixture  per  20  grams  of  weight. 

The  poison  will  be  borne.  It  has  been  neu- 
tralized by  the  serum  of  the  immune  animal. 
This  result  accords  with  the  discovery  of  Behring 
and  Kitasato  that  immunity  in  diphtheria  and 
tetanus  depends  on  the  power  of  the  serum  to 
neutralize  the  poison. 

2.  Divide  the  second  portion  of  the  antitoxine 
blood  among  six  small  test-tubes.  To  the  first 
add  a  few  drops  yo'oVo o"  ri°m  solution.  To  the 
others  add  amounts  increasing  in  a  definite  ratio. 

At  first  there  will  be  no  effect  (immunity). 
As  the  amount  of  ricin  added  is  increased,  a  point 
will  be  reached  at  which  agglutination  of  red 
corpusles  will  be  produced.  This  is  the  neutrali- 
zation point. 

Evidently,  there  is  a  definite  quantitative 
chemical  relation  between  the  toxine  and  the 
antitoxine. 


222         THE  INCOME  OF  ENERGY 

Theory  of  Immunity.1  —  Jenner  discovered  the 
protective  action  of  vaccinia  against  small-pox.  The 
sni all-pox  virus  when  passed  through  a  susceptible 
animal  becomes  attenuated.  This  weakened  poison 
introduced  into  the  circulation  in  man  protects  the 
individual  for  long  periods  against  the  original  disease 
—  it  establishes  an  artificial  immunity  against  small- 
pox. Schwann  found  that  fermentation  and  putre- 
faction arose  through  the  agency  of  micro-organisms 
coming  from  without.  Pasteur  and  Koch  demonstrated 
that  the  inoculation  of  animals  with  pure  cultures  of 
certain  bacteria  produced  specific  infectious  diseases, 
and  that  these  cultures  could  be  modified  at  will, 
either  by  passing  through  the  animal  body,  as  in 
Jenner's  method,  or  in  artificial  culture  media.  Pas- 
teur produced  artificial  immunity  by  using  attenuated 
virus.  Behring  discovered  that  the  blood-serum  of 
animals  immunized  against  diphtheria  contained  a  sub- 
stance which  would  protect  other  animals  against  the 
toxine  of  diphtheria.  So  also  with  tetanus.  Ehrlich 
introduced  the  quantitative  study  of  toxines  and  anti- 
toxines  by  means  of  test-tube  experiments,  thereby 
eliminating  the  uncertain  factor  of  the  animal  body. 
Thus  it  was  shown  in  experiments  on  tetanus  toxine 
that  the  action  of  antitoxines  is  accelerated  by  heat, 
retarded  by  cold,  dependent  on  concentration  —  in 
short,  that  it  is  a  chemical  action.  In  the  above  ex- 
periments   on   ricin,    it   is   shown    that   the    relation 

1  Ehrlich :  Croonian  Lecture,  Proceedings  of  the  Royal 
Society,  London,  1901,  lxvi,  pp.  424-448. 


FERMENTATION  223 

between  toxine  and  antitoxine  is  quantitative.  These 
results,  obtained  by  test-tube  experiments,  have  been 
confirmed  by  observations  on  living  animals.  Thus  it 
was  established  that  a  fixed  quantity  of  toxine  is  neu- 
tralized by  a  fixed  quantity  of  its  specific  antitoxine. 

Chemical  substances  affect  only  those  tissues  with 
which  they  are  able  to  come  into  chemical  contact. 
They  must  first  reach  the  tissue.  This  general  law  is 
illustrated  by  the  experiments  of  Douitz  with  tetanus 
toxine.1  When  the  toxine  is  injected  directly  into 
the  circulation  and  immediately  followed  by  a  chemi- 
cally equivalent  amount  of  antitoxine,  the  animal  is 
not  poisoned  ;  all  the  toxine  circulating  in  the  blood 
is  neutralized.  When  the  same  neutralizing  dose  is 
injected  eight  minutes  after  the  toxine,  death  occurs 
from  tetanus  exactly  as  if  no  antitoxine  had  been  used. 
In  these  eight  minutes  a  lethal  quantity  of  toxine 
must  have  left  the  blood  and  entered  the  tissues. 
This  toxine  which  has  entered  the  tissues  may  still 
for  a  time  be  withdrawn  by  injection  of  the  specific 
antitoxine  in  quantities  much  greater  than  the  simple 
neutralizing  dose.  The  longer  the  delay,  the  larger 
the  saving  dose.  But  after  a  fixed  interval,  or  "period 
of  incubation,"  no  amount  of  antitoxine,  however 
large,  will  prevent  tetanus.  There  must,  therefore, 
be  present  in  the  brain  or  cord  (the  organ  princi- 
pally affected  by  tetanus  toxine)  certain  atom  groups 
which,  like  the  antitoxine,  have  a  chemical  affinity 
for  the  toxine.     At  the  close  of  the  period  of  incuba- 

1  Donitz  :  Klinisches  Jahrbuch,  1900,  vii. 


224         THE  INCOME  OF  ENERGY 

tion  the  chemical  union  between  these  atom  groups 
and  the  toxine  is  complete  and  the  antitoxine  is  shut 
out.  Wassermann  1  found  that  when  tetanus  toxine 
was  mixed  with  fresh  brain  or  cord  substance  from  the 
guinea-pig,  the  toxine  united  chemically  with  the  nerve 
centres  so  that  neither  the  surrounding  liquid  nor  the 
mixture  itself  was  poisonous  when  injected  into  an 
animal. 

The  stable  benzene  ring  and  the  less  stable  side-chains 
of  the  benzene  derivatives 2  suggested  to  Ehrlich  that 
living  cells  also  consist  of  a  stable  centre  and  less  stable 
side-chains.  The  side-chains  enable  the  cell  to  form 
chemical  combinations  with  food  stuffs  and  other  bodies 
that  possess  atom  groups  having  a  chemical  affinity 
with  the  atom  groups  in  the  side-chains.  It  is  in  this 
way  that  the  toxine  is  bound  to  the  cell.  Experiments 
have  shown  that  the  binding  atoms  in  the  toxine 
molecule  are  not  the  poison  atoms.  If  for  a  portion 
of  fresh  toxine  there  be  determined  quantitatively  (1) 
the  killing  power  and  (2)  the  amount  of  antitoxine 
required  to  neutralize  the  toxine,  and  if  the  remainder 
of  the  toxine  be  then  allowed  to  stand  for  a  time,  it 
will  be  found,  on  again  determining  the  toxic  power 
and  the  combining  power,  that  the  toxic  power  has  di- 
minished, while  the  combining  power  remains  almost 
the  same.  Hence,  two  separate  and  independent  groups 
exist.  Ehrlich  terms  the  combining  atoms  the  hapto- 
phore  group,  while  the  poison  atoms  are  the  toxophore 

1  Wassermann  :  Berliner  klinische  Wochenschrift,  1898. 

2  Seepage  216. 


FERMENTATION  225 

group.  The  haptophore  atom  group  (Sltttw,  I  cling  to) 
unites  with  the  antitoxine,  if  there  be  any  present,  or 
with  any  other  atom  group  for  which  it  lias  chemical 
affinity.  If  this  latter  atom  group  be  in  the  side-chain 
of  a  living  cell,  its  union  with  the  haptophore  atoms 
of  the  toxine  will  necessarily  bring  the  poison  atoms  of 
the  toxine  into  intimate  chemical  relationship  with  the 
central  atoms  of  the  cell.  Poisoning  will  then  take 
place.  If  the  cells  of  vital  organs  have  no  atom  groups 
with  chemical  affinity  for  the  haptophore  group  of  a 
toxine,  no  union  between  cell-atom  group  and  hapto- 
phore takes  place,  the  toxophore  is  not  brought  into 
intimate  contact  with  the  cell,  and  poisoning  does 
not  occur.  The  animal  is  naturally  immune  to  this 
particular  toxine.  Thus  a  toxine  in  sausages  is  exces- 
sively poisonous  to  man,  the  monkey,  and  the  rabbit, 
while  even  large  amounts  are  not  injurious  to  the 
dog. 

The  haptophore  group  of  the  toxine  acts  immediately 
after  injection  into  the  organism,  while  in  most  or  all 
toxines  the  toxophore  group  becomes  active  only  after 
a  longer  or  shorter  incubation  period.  During  this 
period  the  animal  may  often  be  saved  by  placing  it  in 
conditions  in  which  the  toxophores  cannot  act.  Thus 
frogs  kept  at  less  than  20°  C.  are  not  poisoned  by  large 
doses  of  tetanus  toxine,  though  much  smaller  doses  are 
fatal  at  a  higher  temperature  (Morgenroth). 

The  toxophile  atom  group  of  the  cell  was  not  pre- 
destined to  unite  with  a  remotely  possible  toxine,  — 
it  has  a  normal  function,  probably  that  of  attaching 
food   to  the  cell.     When   it  enters  into  its  firm  and 

15 


226         THE  INCOME  OF  ENERGY 

enduring  union  with  the  haptophore  group  of  a  toxine, 
this  normal  function  is  lost.  Such  a  loss  acts  as  a 
physiological  stimulus.1  New  side-chains  are  produced 
by  the  cell,  only  to  unite  with  fresh  toxine.  The  pro- 
duction and  the  loss  of  side-chains  continue  until  all 
the  toxine  in  the  blood  is  neutralized.  By  this  time 
the  cell  has  become  habituated  to  a  more  than  normal 
production  of  these  special  atom  groups.  The  excess 
is  cast  off  like  a  secretion  and  circulates  in  the  blood. 
These  free  side-chains,  possessing  a  special  affinity  for 
one  specific  toxine,  constitute  the  antitoxine  of  that 
toxine. 

Their  continued  production  after  the  neutralization 
of  all  the  toxine  protects  the  animal  against  fresh 
toxine,  i.  e.  establishes  continued  immunity. 

It  has  already  been  stated  that  by  special  means  the 
toxophore  group  of  a  toxine  may  be  weakened  or 
destroyed  while  its  haptophore  group  is  unchanged. 
Such  altered  and  non-poisonous  toxines  are  termed 
toxoids.  As  their  affinity  for  the  side-chains  of  the 
cells  remains  unaltered,  the  toxoids  by  continuing  to 
unite  with  the  side-chains  of  the  cells  may  stimulate 
the  production  of  such  side-chains  in  excess,  or,  in 
other  words,  may  assist  in  making  antitoxine  and  thus 
establishing  immunity. 

1  Weigert :  Deutsche  medicinische  Wochenschrift,  1896. 


fermentation  227 

Haemolytic  and  Bacteriolytic  Ferments 

Bordet's  Experiments.1  —  Inject  into  the  perito- 
neum of  a  guinea-pig  10  c.c.  defibrinated  rabbit 
blood  on  five  successive  days.  After  two  more 
days  bleed  the  guinea-pig  and  obtain  the  serum, 
by  allowing  the  blood  to  stand  in  test-tubes  in  a 
cool  place  until  the  shrinking  clot  has  pressed 
out  the  serum. 

1.  Mix  a  drop  of  serum  from  a  fresh  guinea- 
pig  (one  not  injected  with  rabbit  blood)  with  a 
drop  of  defibrinated  rabbit  blood  and  examine 
under  the  microscope.  The  corpuscles  show  a 
very  slight  agglutination,  but  are  otherwise  un- 
injured. The  normal  serum  of  the  guinea-pig  is 
almost  inactive  upon  rabbit  blood. 

2.  A.  Mix  a  drop  of  the  serum  from  the 
injected  guinea-pig  with  a  drop  of  defibrinated 
rabbit  blood  and  examine  under  the  microscope. 
The  corpuscles  are  strongly  agglutinated.2 

B.  Mix  0.5  c.c.  of  the  serum  with  1.5  c.c. 
defibrinated  rabbit  blood. 

1  Bordet :  Annales  de  1'Institut  Pasteur,  1898,  xii,  pp.  692- 
694. 

2  Agglutinated  blood  looks  granular,  especially  on  gentle 
shaking  ;  the  massed  corpuscles  sink  rapidly ;  they  will  not  pass 
through  filter  paper.  Agglutination  of  blood  corpuscles  is 
similar  to  the  clumping  of  the  typhoid  bacillus  in  the  serum  of 
a  typhoid-fever  patient. 


228         THE  INCOME  OF  ENERGY 

The  corpuscles  are  agglutinated  and  their  hae- 
moglobin is  set  free.  The  mixture  becomes  red, 
clear  and  limpid  in  two  or  three  minutes.  With 
the  microscope  nothing  can  be  found  but  the 
stroma  of  the  corpuscles,  more  or  less  deformed, 
very  transparent  and  scarcely  visible. 

The  continued  presence  of  blood  corpuscles 
of  the  rabbit  in  the  blood  of  the  guinea-pig  has 
developed  in  the  latter  the  power  to  agglutinate 
the  corpuscles  and  to  set  free  their  haemoglobin. 
It  is  thus  that  the  guinea-pig  protects  itself ;  it 
acquires  immunity. 

3.  Heat  1  c.c.  of  serum  to  55°  C.  for  half  an 
hour.  Add  0.5  c.c.  of  this  to  1 .5  c.c.  defibrinated 
rabbit  blood  as  in  Experiment  2  B. 

The  serum  which  was  heated  to  55°  C.  no 
longer  destroys  the  corpuscles,  but  still  strongly 
agglutinates  them.1 

Evidently  the  agglutination  of  the  corpuscles 
and  the  setting  free  of  the  haemoglobin  (termed 
"laking")  are  effected  by  different  substances. 
The  agglutinating  body  resists  a  temperature  that 
destroys  the  blood-laking  body. 

4.  To  the  mixture  used  in  the  preceding  experi- 
ment, add  2  c.c.  of  fresh  serum  from  a  normal 

1  A  very  slow  destruction  of  the  red  corpuscles  may  be  ob- 
served. This,  however,  is  due  to  the  fresh  serum  in  the  1.5 c.c. 
defibrinated  rabbit  blood,  as  will  be  evident  from  Experiment  4. 


FERMENTATION  229 

guinea-pig  (one  that  has  not  been  injected  with 
rabbit  blood). 

In  a  few  minutes  the  mixture  becomes  limpid 
and  red.     The  laking  power  is  restored. 

Obviously,  with  the  fresh  serum  was  added 
the  unstable  body  destructive  to  red  corpuscles. 
Ehrlich  and  Morgenroth  have  shown  that  at  low 
temperatures  the  stable  body  unites  with  the  red 
corpuscles  while  the  unstable  body  remains  in 
the  serum ;  in  this  case  the  haemoglobin  is  not 
set  free.  At  higher  temperatures  the  haemoglo- 
bin separates  and  the  unstable  body  is  found  to 
have  left  the  serum.  It  has  joined  the  stable 
body  in  the  sediment. 

Following  the  side-chain  theory  already  men- 
tioned, Ehrlich  and  Morgenroth  assume  that  the 
stable  substance  has  two  combining  powers; 
on  the  one  hand  it  unites  with  the  red  corpus- 
cles, on  the  other  with  the  unstable  substance, 
thus  bringing  it  to  the  cell  which  it  may  then 
destroy. 

Immunity  against  toxines  and  foreign  red  cor- 
puscles are  only  two  of  the  protective  actions  of 
the  blood.  The  injection  of  cells  of  the  most 
varied  kinds  is  followed  by  the  production  of 
specific  protective  bodies;1  thus,  the  injection  of 

1  Metchnikoff:  Annales  de  l'lnstitut  Pasteur,  1900,  xiv, 
p.  369. 


230        THE  INCOME  OF  ENERGY 

bacteria  causes  the  formation  of  bacteriolysines, 
which  destroy  the  injurious  organism. 

Many  haemolysines  and  agglutines  are  found 
in  plants  ;  others,  for  example,  the  tetanus  bacil- 
lus, are  bacterial;  still  others,  such  as  snake 
venom,  are  animal  secretions. 

Oxidizing  Ferments 

Schdnbein's  Experiment.1 —  1.  To  five  c.  c.  hy- 
drogen peroxide  add  tincture  of  guiac  (freshly 
prepared  by  dissolving  guiac  resin  in  alcohol) 
drop  by  drop  until  the  liquid  is  milky.  Now 
add  from  eight  to  ten  drops  of  a  somewhat  con- 
centrated extract  of  malt,  prepared  in  the  cold. 

The  guiac  will  be  oxidized  and  will  turn  blue. 

2.  Eepeat  the  experiment,  adding  in  place  of 
the  malt  extract  from  eight  to  ten  drops  of  blood. 

The  guiac  will  be  oxidized,  as  before. 

Further  Oxidations  by  Animal  Tissues.2  — 
1.  Soak  strips  of  bibulous  paper  in  a  diluted  solu- 
tion made  as  follows : 

a-naphthol 1  mol. 

sodium  carbonate    ....     3     " 
para-phenylenediamine     .     .      1     " 

1  Schonbein  :  Zeitschrift  fur  Biologie,  1868,  iv,  p.  367. 

2  Spitzer  :  Arcbiv  fur  die  ge.sannnte  Physiologie,  1895,  lx, 
pp.  322-323. 


FERMENTATION  231 

This  solution,  left  in  the  atmosphere,  oxidizes 
slowly  to  indophenol  (violet  color). 

Place  a  drop  of  a  known  oxidizer,  e.g.  ferri- 
cyanide  of  potash  or  potassium  bichromate,  on 
the  saturated  paper. 

The  color  will  change  at  once,  in  consequence 
of  immediate  oxidation. 

(1)  C6FT4(NH2)2  +  C10H7OH  +  0  = 

PARA-PHENYLENEDIAMINE       A-NAPHTHOL  CcTrLNHo 

NH<C10H6OH  +  H*° 

(2)  NH<C6H4NH2  +  0  =  N<C°H*NH*  +H.0 

C10H6OH  I      C10H6O 


INDOPHENOL 

Each  of  the  combining  molecules  has  been  acted 
upon  by  a  different  oxygen  atom;  hence  the  oxy- 
gen molecule  must  have  been  split. 

2.  Eub  the  test  paper  with  finely  divided  tissue 
from  the  liver  or  any  other  organ. 

Oxidation  will  occur. 

A  drop  of  blood  placed  on  the  test  paper  is 
soon  surrounded  by  a  characteristically  colored 
ring. 

Extraction  of  Nucleo-Proteid  from  Liver}  — 
Perfuse  a  fresh  liver  (dog)  with  tap  water  until 
the  washings  are  no  longer  colored  by  haemo- 

1  Spitzer  :  Archiv  fur  die  gesammte  Physiologie,  1897,  lxvii, 
p.  616. 


232        THE  INCOME  OF  ENEEGY 

globin.  Grind  the  liver  to  a  pulp  and  press 
through  several  thicknesses  of  gauze.  Add  five 
volumes  of  distilled  water.  Allow  the  mixture 
to  stand  twenty-four  hours  at  low  temperatures. 
Remove  the  opalescent  watery  extract  with  a 
pipette  and  filter  through  linen.  Demonstrate 
with  the  microscope  that  liver  cells  are  absent 
from  the  liquid.  Add  T^  HC1  drop  by  drop  until 
there  is  no  further  precipitation,  and  the  super- 
natant fluid  is  clear.  Since  the  precipitate  redis- 
solves  in  acid,  use  lacmoid  as  an  indicator.  Cease 
when  the  lacmoid  shows  a  trace  of  excess.  De- 
cant the  precipitate,  filter,  wash  the  residue  with 
water. 

Oxidation  by  Nucleo-Proteid.  —  Place  in  a  wide- 
necked  flask  50  c.c.  water  containing  0.2  gram 
of  the  fresh,  brown  substance  and  10  c.c.  hydro- 
gen peroxide  in  a  small  glass  cup.  The  hydrogen 
peroxide  must  be  neutralized  with  from  1  to  1.5 
c.c.  {\  NaOH.  Connect  the  flask  with  the  lower 
end  of  a  eudiometer  by  means  of  a  bent  tube. 
Shake  the  flask  so  that  the  hydrogen  peroxide 
shall  come  in  contact  with  the  tissue.  Oxygen 
is  at  once  set  free.  Kead  in  the  eudiometer 
the  oxygen  developed  from  minute  to  minute. 
Spitzer  found : 

After  minutes  .  .  1  2  3  4  5  8  9  1G 
C.c.    02  developed    19    28    41     55    69    85    87    95 


FERMENTATION  233 

Oxidation  about  the  Nucleus.1  —  Introduce  the 
oxidizable  solution  of  a-naphthol  and  para-phe- 
nylenediamine  (page  230),  beneath  the  cover 
glass  of  a  fresh  preparation  of  teased  thymus 
or  spleen. 

"  Granules  of  the  intense  greenish-blue  oxi- 
dation product  shortly  make  their  appearance 
within  the  leucocytes.  Their  first  appearance  is 
typically  at  the  boundary  between  nucleus  and 
cytoplasm ;  eventually  the  latter  may  become 
so  densely  laden  as  completely  to  obscure  the 
nucleus.  .  .  .  The  nucleus  is  the  chief  agency  in 
the  intracellular  activation  of  oxv^en.  The  ac- 
tive  or  atomic  oxygen  is  in  general  most  abun- 
dantly freed  at  the  surface  of  contact  between 
nucleus  and  cytoplasm." 

Glycolysis  in  Blood.  Bernard's  Experiment?  — 
125  c.c.  dog's  blood  were  divided  into  five  equal 
parts.  The  sugar  in  each  was  estimated  as 
follows : 

Sugar 
Grams  per  1000. 

1.07 


1.  Analysis  made  at  once 

2.  "  "      after  10  minutes 

3.  "  "         "     30        " 

4.  "  "  "       5  hours     . 
5           (t           "         "     24      " 


1.01 

0.88 
0.44 
0.00 

vii,  p.  420. 


1  Lillie  :  American  journal  of  physiology,  1902, 

2  Bernard :  Comptes  rendus  de  1'ae.ademie  des  sciences,  Paris, 
1876,  lxxxii,  p.  1406. 


234  THE   INCOME   OF    ENERGY 

Sugar    disappears    from    the   blood   on   stand- 


ing. 


It  has  been  found  by  Lepine  and  Barral 1  that 
the  glycolytic  power  of  the  blood  increases  as  the 
temperature  rises  to  52.5°  C,  which  is  the  opti- 
mum.    At  54°  the  ferment  is  destroyed. 

Oxidation  not  Dependent  on  Living  Cells  of  Blood. 
—  Place  the  following  solutions  at  34-35°  C.  for 
six  hours,  allowing  a  stream  of  air  to  pass  through 
the.  liquid.     Then  estimate  the  sugar.2 

A.    Calf's  blood 100  c.c. 

Water  containing  1.14  gram  grape  sugar        10  c.c. 
Seegen  3  recovered  1.000  gram. 

1  Lepine  and  Barral :  Comptes  rendus  de  l'academie  dea  sci. 
ences,  Paris,  1891,  cxii,  p.  146. 

2  Test  the  filtrate  by  adding  a  drop  of  acetic  acid  and  a  little 
ferrocyanide  of  potassium. 

The  absence  of  a  precipitate  shows  freedom  from  proteids  and 
ferric  salts.     Concentrate  filtrate  to  150-200  c.c. 

Titration  of  the  Sugar  Extract.  —  Make  the  volume  of  the 
solution  such  that  its  probable  content  of  sugar  shall  lie 
between  0.0004  and  0.0010.  Causse  (Bulletin  de  la  Societe 
chimique  de  Paris,  1,  p.  625)  recommends  that  1750  c.c.  of 
water  containing  5  grams  of  ferrocyanide  of  potassium  be  added 
to  each  250  c.c.  of  Fehling's  solution.  Boil  10  c.c.  of  this 
mixture,  and  add  the  sugar  solution  drop  by  drop  until  the  bin* 
liquid  is  decolorized  (Arthus  :  Archives  de  physiologie,  1891, 
p.  425). 

3  Estimation  of  Sugar  in  Blood.  Extraction  of  the  Sugar 
from  the  Blood.  — To  350-400  c.c.  boiling  water  add  all  at  once 
50  c.c.  blood  containing  5  c.c.   one  per  cent  acetic  acid.     Let 


FERMENTATION  235 

B.    Calf's  blood 100  c.c. 

Water  containing  1.14  gram  grape  sugar  10  c.c. 

Chloroform 1  c.c. 

Seegen  recovered  0.960  gram. 

The  chloroform  destroys  the  cells,  but  fails  to 
check  the  oxidation. 

Relation  of  Glycolysis  to  the  Pancreas  and  the 
Lymph.1  —  Remove  the  pancreas  aseptically  from  an 
anaesthetized  dog  which  has  fasted  thirty-six  hours. 
Estimate  the  sugar  in  the  urine  at  intervals  of  a  few- 
hours. 

Sugar  will  be  present  in  large  and  increasing  quanti- 
ties,2 rising  even  to  twenty  per  cent. 

Inject  into  the  jugular  vein  15-20  c.c.  of  lymph 
from  the  thoracic  duct  of  a  dog  fed  a  few  hours  before 
upon  one  litre  of  milk. 

the  mixture  boil  for  a  few  minutes.     Filter  through  a  small 
linen  cloth. 

Separation  of  Proteids.  —  Boil  the  filtrate.  Most  of  the  pro- 
teids  will  separate  by  coagulation.  The  remainder,  if  necessary, 
may  be  removed  by  adding  to  each  300  c.c.  of  filtrate,  5  c.c. 
saturated  solution  of  sodium  acetate,  and  a  small  quantity  of  a 
dilute  solution  of  ferric  chloride,  neutralizing  almost  completely 
with  dilute  soda  solution,  and  boiling.  The  ferric  chloride  will 
precipitate  as  ferrous  chloride  and  will  carry  down  the  last 
traces  of  proteid  substances.  Filter.  Wash  with  boiling  water. 
(Seegen  :  Centralblatt  fur  Physiologic,  1891,  v,  p.  824.) 

1  Lepine  :  Comptes  rendus  de  l'academie  des  sciences,  Paris, 
1890,  ex,  p.  742. 

2  Von  Mering  and  Minkowski :  Archiv  fur  experimentelle 
Pathologie  und  Pharmakologie,  1890,  xxvi,  p.  371. 


236        THE  INCOME  OF  ENERGY 

The  glycosuria  will  greatly  diminish. 

After  a  few  hours,  the  glycosuria  will  become  once 
more  intense,  continuing  until  death.  The  quantity  of 
sugar  in  the  blood  is  also  greatly  increased. 

Glycolytic  Ferment  of  Pancreas.1  —  Remove  the 

pancreas  aseptically  from  a  dog  immediately  after 
death.  Crush  it  at  once  in  100  c.c.  sterile  water 
containing  0.2  gram  sulphuric  acid.  Allow  it  to 
macerate  two  hours  at  38°  C.  Neutralize  the 
acid  with  soda,  add  0.5  gram  pure  glucose,  and 
keep  the  mixture  one  hour  at  38°  C.  Estimate 
the  sugar. 

The  loss  will  be  from  ten  to  fifty  per  cent. 

When  pancreatic  extract  made  without  acid  is  used, 
the  loss  of  sugar  is  much  less.  Probably,  therefore, 
the  glycolytic  ferment  is  produced  from  a  zymogen  by 
hydration. 

Malt  diastase,  or  salivary  diastase,  kept  three  hours 
at  38°  in  water  containing  one  tenth  per  cent  sulphuric 
acid  loses  the  power  to  change  starch  to  sugar,  but  ac- 
quires a  glycolytic  power. 

If  the  pancreatic  juice  which  flows  upon  stimulation 
of  the  peripheral  end  of  the  vagus  (Pavvlow)  is  treated 
with  dilute  acid,  1  :  1000,  the  amylolytic  power  is  lost, 
but  glycolytic  power  is  acquired.  During  the  excita- 
tion of  the  nerve  —  while  the  juice  is  flowing  —  the 

1  Lepine  :  Comptes  rendus  de  l'academie  des  sciences,  Paris, 
1895,  cxx,  p.  139. 


FERMENTATION  237 

blood  in  the  pancreatic  vein  has  almost  no  glycolytic 
power;  after  the  juice  ceases  to  run,  the  blood  has 
considerable  glycolytic  power.  Here  the  external  is 
balanced  against  the  internal  secretion  of  the  pancreas. 

Oxidative  ferments  are  very  widely  distributed  both 
in  animals  and  plants.  The  above  experiments  show 
their  presence  in  the  blood;  pancreas,  liver,  and  lymph. 
They  are  present  also  in  the  urine. 

The  stomach  contains  a  ferment  that  oxidizes  lactose 
to  lactic  acid.1 

Urushi,  the  milky  secretion  of  Rhus  vernicifera,  dries 
in  the  air  to  a  translucent  varnish  (Japanese  lacquer). 
It  contains  urushic  acid,  which  does  not  dry  sponta- 
neously, and  a  ferment,  the  addition  of  which  to 
urushic  acid  causes  the  latter  to  dry  to  lacquer.  A 
sample  of  fresh  juice  boiled  to  stop  the  action  of  the 
ferment  on  urushic  acid  contained  15.01  per  cent 
oxygen  ;  lacquer  dried  in  the  usual  manner  contained 
20.52  per  cent  oxygen. 

Many  oxidations  are  effected  by  the  tissues  without 
the  aid  of  ferments,  so  far  as  is  yet  known.  These  be- 
long properly  to  metabolism,  but  in  passing,  it  may  be 
noted  that  while  substances  exceedingly  resistant  to 
oxidation,  for  example,  proteids,  are  oxidized  in  the 
body,  other  substances  very  easily  oxidizable  may  be 
excreted  unchanged  ;  oxalic  acid  is  one  of  these.2 

1  Hammarsten  :  Maly's  Jahresbericht  der  Thierchemie,  1872, 
ii,  p.  118.       (Original  in  Swedish.) 

2  Pohl :  Archiv  fur  experimentelle  Pathologie  und  Pharraa- 
kologie,  1896,  xxxvii,  p.  413. 


238         THE  INCOME  OF  ENERGY 

Hoppe-Seylers  Theory.1  —  Living  tissues  consist  of 
easily  combustible  reducing  substances,  which  split 
the  oxygen  molecules,  taking  to  themselves  one  atom 
of  0  and  setting  the  other  free  in  active  state  to 
unite  with  any  oxidizable  substance  present. 

Traube's  Theory.2 — In  living  protoplasm  oxygen  is 
rendered  active  by  an  oxidizing  ferment,  which  brings 
the  oxygen  to  bodies  ordinarily  oxidizable  only  by  such 
powerful  agents  as  heat  and  strong  alkalies. 

Inorganic  bodies,  e.  g.  platinum  black,  the  oxides  of 
copper,  silver,  mercury,  and  vanadium,  and  certain  iron 
salts  similarly  act  as  oxygen  carriers.     Thus 

(1)  Pt  +  02  +  H2  =  PtO  +  H20 

(2)  PtO  +  H2  =  Pt  +  H20 

The  oxygen  carrier  reduces  H202,  takes  one  atom  0 
to  itself,  then  gives  off  this  atom  in  an  active  or 
nascent  state  to  oxidize  any  oxidizable  compound 
present ;  e.  g.  guiac.  Grape  sugar  takes  0  from 
indigo-blue,  producing  thereby  indigo-white.  The 
indigo-white  oxidizes  itself  to  indigo-blue,  then  gives 
up  another  atom  of  0,  and  so  on. 

Alcoholic  Fermentation 
The  Yeast  Plant.  —  Observe  a  solution  of  sugar 
undergoing   alcoholic   fermentation.3      Note    the 
bubbles  of  gas,  the  scum,  the  sour  odor. 

1  Hoppe-Seyler:  Zeitschrift  fur  physiologische  Chemie,  1879, 
ii,  p.  1. 

'2  Traube  :  Berichte  der  deutschen  chemischen  Gesellschaft, 
1883,  xvi,  pp.  123, 1201,  and  earlier  papers  in  volumes  x  and  xv. 

8  The  fermentation  is  assisted  by  providing  the  yeast  plant 


FERMENTATION  239 

Examine  some  of  the  mixture  under  the  micro- 
scope. Xote  the  multitude  of  globular  or  slightly 
ovoid  bodies,  the  largest  about  T^o  mm-  m  diame- 
ter. They  are  motionless.  Many  have  put  forth 
buds.     They  seem  to  be  plants  in  active  growth.1 

1.  Place  300  c.c.  of  the  nutrient  liquid  (Ex- 
periment 1)  in  a  flask  holding  500  c.c.  Add  a 
piece  of  fresh  compressed  yeast  the  size  of  a  pea. 
Place  the  flask  in  a  temperature  of  35°  C. 

Note  that  as  fermentation  advances  the  yeast 
increases  in  quantity. 

2.  Place  a  small  piece  of  fresh  compressed 
yeast  in  a  test-tube.  Fill  the  tube  with  nutrient 
liquid  and  invert  it  in  a  dish  of  similar  liquid.  The 
tube  may  be  kept  upright  by  a  elamp.  Let  the 
mixture  stand  twenty -four  hours  in  a  warm  room. 

with  the  salts  present  in  the  ash  of  yeast  (Pasteur).     A  useful 
substitute  is 

Potassium  phosphate     ...  20  gms. 

Calcium  phosphate         ...  2 

Magnesium  sulphate      ...  2 

Ammonium  tartrate       .     .     .         100 

Cane  sugar 1,500 

Water 8,376 

10,000 
(Practical  biology,  Huxley  and  Martin.) 
1  Cagniard-Latour  :  L'Institut,  1835,  iii,  p.  150  ;  also  Annales 
de  chimie  et  de  physique,  1838,  Ixviii,  p.  206.  The  yeast  plant 
was  first  observed  microscopically  in  beer-yeast  by  Leeuwen- 
hoek,  1680,  but  he  did  not  associate  fermentation  with  the 
growth  of  the  yeast. 


240         THE  INCOME  OF  ENERGY 

The  tube  will  fill  with  gas.  With  a  bent  pipette 
introduce  about  1  c.c.  of  a  solution  of  sodium 
hydroxide  (sp.  gr.  1.12  =  11  per  cent).  The  gas 
will  be  absorbed,  with  formation  of  sodic  carbon- 
ate, and  the  liquid  will  rise  in  the  tube. 

The  growth  of  the  yeast  plant  is  accompanied 
by  the  production  of  carbon  dioxide. 

3.  Eeturn  to  Experiment  1.  After  the  fer- 
menting liquid  has  ceased  to  give  off  gas,  place  a 
stopper  with  a  bent  tube  in  the  mouth  of  the 
flask  and  distill  the  contents  of  the  flask  in  a 
water  bath.  Condense  the  first  fifth  of  the  dis- 
tillate. Saturate  this  with  sodium  carbonate. 
Eedistill,  and  condense. 

Test  for  alcohol  by  warming  the  distillate  with 
potassium  dichromate  and  dilute  sulphuric  acid, 
whereby  the  alcohol  will  be  oxidized  to  aldehyde, 
with  characteristic  odor. 

Alcohol  is  present. 

The  production  of  alcohol  by  the  yeast  is  the  work 
of  the  ferment  zymase.1  This  body  is  closely  bound 
to  the  protoplasm  of  the  cell,  very  easily  destroyed,  not 
produced  in  excess,  and  not  secreted  free.  Only  sugars 
containing  three,  six,  and  nine  carbon  atoms  are  at- 
tacked. The  saccharobioses  must  be  "  inverted  "  be- 
fore they  can  be  fermented.     Thus,  cane  sugar  must 

1  Buchner  :  Berichte  der  deutschen  cheuiischen  Gesollscliaft, 
1897,  xxx,  pp.  117,  1110,  2668. 


FERMENTATION  241 

first  he  inverted  to  grape  sugar  by  invertin,1  and 
malt  sugar  by  maltase.  Lactase  is  present  in  some 
yeasts,  enabling  them  to  ferment  milk  sugar.  Diastase 
is  also  found. 

The  action  of  these  several  ferments  becomes  clear 
when  the  chemical  nature  of  the  carbohydrates  is 
recalled. 

Chemical  Relations  of  Carbohydrates.  — Carbohy- 
drates were  formerly  defined  to  be  compounds  con- 
taining six,  or  a  multiple  of  six  carbon  atoms,  together 
with  hydrogen  and  oxygen  atoms  in  the  proportion  in 
which  they  exist  in  water.  The  researches  of  E. 
Fischer  have  shown  that  all  aldehydes  (bodies  which 
are  the  first  oxidation  products  of  primary  alcohols,  and 
which  contain  the  carbonyl  group  CO)  and  all  ketones 
(bodies  which  are  the  first  oxidation  products  of  second- 
ary alcohols  and  which  likewise  contain  the  carbouyl 
group  CO)  contain  carbon,  hydrogen,  and  oxygen,  there 
being  two  atoms  of  hydrogen  to  one  atom  of  oxygen, 
as  in  water. 

The  carbohydrates,  therefore,  no  longer  occupy  an 
isolated  position,  but  are  to  be  classed  with  the  fats, 
being  methane  derivatives  in  which  the  carbon  atoms 
are  arranged  in  an  open  chain;  thus,  grape  sugar  is  an 
aldehyde  alcohol,  and  fruit  sugar  a  ketone  alcohol. 

The  carbohydrates  are  divided,  according  to  the  size 
of  their  molecule,  into  monosaccharides,  disaccharides, 
and  polysaccharides.     The  monosaccharides  (e.  g.  grape 

1  For  extraction,  see  Lea  :  Journal  of  physiology,  1885,  vi, 

p.  142. 

16 


242 


THE    INCOME    OF    ENERGY 


sugar)  are  the  first  oxidation  products  of  the  hexahy- 
dric  alcohols  ;  the  higher  carbohydrates  are  anhydrides 
of  the  monosaccharides.  Most  of  the  higher  carbohy- 
drates cannot  be  fermented  directly,  but  must  first 
be  hydrolyzed  (i.  e.  take  up  water).  This  hydrolysis 
may  be  accomplished  by  the  prolonged  action  of  dilute 
acids  at  high  temperatures,  by  the  action  of  water  at 
still  higher  temperatures,  or  by  specific  ferments,  e.  g. 
diastase,  at  the  relatively  low  temperature  of  the  body. 
The  polysaccharides,  consisting  of  the  starches,  the 
gums  (e.  g.  dextrine  or  starch  gum)  and  the  celluloses 
(wood  fibre)  differ  greatly  from  the  lower  carbohy- 
drates. The  polysaccharides  are  usually  amorphous 
and  are  not  easily  soluble  in  water. 


Carbohydrates.1 


Glucoses,  Monoses 
C6H1206. 

Saccharobioses 

Polysaccharides 

(C6H10O5)x. 

Grape  sugar — 

— 

-Malt  sugar — 

— Starch 

Grape  sugar — 

— 

Grape  sugar — 

— 

-Cane  sugar 

Fruit  sugar — 



Grape  sugar — 

— ■ 

Milk  sugar 

Galactose — 

" 

—Dextrine 

1  Richtci's  Organic  Chemistry,  Third  American  Edition,  i, 
p.  121. 


FERMENTATION  243 

The  zymase  attacks  only  those  sugars  which  present 
a  specific  stereo-configuration.  The  position  of  their 
atoms  in  space  must  fit  the  position  of  the  atoms  of 
the  ferment  (the  lock  and  the  key).  Thus,  only  the 
dextro-rotatory  forms  of  the  aldehyde  sugars  (d-glu- 
cose,  d-mannose,  d-galactose)  are  attacked ;  the  sugars 
that  rotate  the  plane  of  polarized  light  to  the  left 
are  not  attacked.  It  is  probable  that  the  zymase 
of  different  species  of  yeast  presents  characteristic  dif- 
ferences. It  is  known  that  the  products  formed  in  the 
fermentation  of  sugar  by  different  species  of  yeasts  are 
to  a  large  degree  characteristic.  Often  these  products 
are  injurious.  Upon  this  specific  action  of  ferments 
rests  the  work  of  Hansen,1  who  taught  the  brewers  to 
make  pure  cultures  of  the  most  favorable  species  of 
yeast,  and  thereby  raised  the  brewing  industry  to  the 
level  of  an  applied  science. 

Activating  Ferments 

Enterokinase.  —  In  1899,  Chepowalnikow, 2  in 
Pawlow's  laboratory,  found  that  pancreatic  juice 
obtained   by  Pawlow's  3  method  contain  ed  very 

1  Hansen  :  Untersuckuugen  an  der  Praxis  der  Gahrungs- 
Industrie,  1895. 

2  Chepowalnikow.:  Thesis  (Russian),  St.  Petersburg,  1899, 
Paris,  1901. 

3  In  Pawlow's  method  the  intestine  is  resected  and  the 
portion  of  the  intestinal  wall  containing  the  opening  of  the 
pancreatic  duct  is  stitched  to  the  edges  of  the  abdominal  wound, 
where  it  soon  unites  ;  the  pancreatic  duct  then  discharges  upon 
the  surface  of  the  abdomen,  where  the  juice  may  be  caught  by 
applying  a  suitable  vessel. 


244         THE  INCOME  OF  ENERGY 

little  trypsin  and  had  a  correspondingly  slight 
action  on  proteids.  When  intestinal  juice  was 
added  to  this  pancreatic  juice,  the  pancreatic 
juice  at  once  became  active  in  proteid  digestion. 
Pawlow  called  the  activating  body  enterokinase.1 
In  1902,  Delezenne  and  Frouin 2  found  that 
pancreatic  juice  obtained  by  catheterizing  the 
pancreatic  duct  contained  no  trypsin  whatever; 
their  procedure  prevented  any  contact  between 
the  juice  and  the  intestinal  mucous  membrane 
at  the  orifice  of  the  pancreatic  duct.  It  has  been 
shown  that  enterokinase  is  a  ferment,  secreted 
in  the  small  intestine,  and  that  it  converts  tryp- 
sinogen  contained  in  pure  pancreatic  juice  into 
trypsin,  the  active  proteid  ferment. 

Preparation  of  Enterokinase.  —  Scrape  lightly 
with  the  handle  of  a  scalpel  the  upper  part  of 
the  mucous  membrane  of  the  small  intestine 
(dog  or  cat).  Digest  the  scrapings  during  two 
days  in  a  closed  vessel  of  water  to  which  a  few 
drops  of  chloroform  have  been  added  to  prevent  de- 
composition. Filter  through  paper,  then  through 
a  Berkefeldt  filter.  The  resulting  solution  is 
perfectly  clear,  contains  a  certain  amount  of 
coagulable   proteid,  and  will  retain   its    activity 

1  Pawlow  :  The  Work  of  the  Digestive  Glands,  translated 
by  W.  H.  Thompson,  1902,  p.  160. 

2  Delezenne  and  Frouin  :  Comptes  rendus  de  la  societe 
de  biologic,  Paris,  1902,  pp.  691-693. 


FERMENTATION  245 

at  room  temperature  for  many  months.  It  is 
rapidly  destroyed  at  35°-40°C.1 

Conversion  of  Trypsinogen  to  Trypsin  by  En- 
terokinase.  —  Place  5  c.c.  of  0.25  per  cent  solution 
of  sodium  carbonate  in  each  of  two  test-tubes 
A  and  B,  containing  gelatine  prepared  by  Fermi's2 
method.  To  A  add  a  few  drops  of  pure  pancreatic 
juice  ; 3  to  B  add  the  same  quantity  of  pure  pan- 
creatic juice  and  a  few  drops  of  enterokinase. 
Place  at  a  temperature  of  30°-35°  C.  The  pure 
juice  will  not  act  on  it,  but  the  juice  to  which 
enterokinase  was  added  will  dissolve  the  gelatine. 
In  order  to  determine  accurately  the  amount  of 
gelatine  dissolved,  the  tubes  often  must  be  cooled 
to  10°  C. 

Absorption  of  Proteids 

Diffusion  of  Proteids  through  Dead   Membrane. 

—  Bend  a  cylinder  of  parchment  paper  and  fasten 
the  ends  to  a  glass  rod.  Place  in  the  parchment 
tubes  thus  formed  25  c.c.  of  each  of  the  follow- 

1  Bayliss  and  Starling:  Journal  of  Physiology,  1903, 
xxx,  p.  80. 

'2  Fermi  and  Repetto  :  Central blatt  flir  Bakteriologie  und 
Parasitenkunde,  1902,  xxxi,  p.  404.  Narrow  glass  tubes,  pref- 
erably graduated,  are  tilled  one  half  full  of  gelatine  (5  to  10 
per  cent)  containing  one  per  cent  of  sodium  fluoride. 

3  Obtained  by  catheterizing  the  pancreatic  duct  of  the  rabbit 
(Rachford's  method),  Journal  of  Physiology,  1891,  xii,  p.  81. 


246 


THE    INCOME    OF   ENERGY 


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248  THE    INCOME   OF   ENERGY 

ing  solutions  : 1  (1)  Egg-albumin,  (2)  Myosin,  (3) 
Alkali-albumin,  (4)  Peptones.  Suspend  the  egg- 
albumin  and  the  peptone  in  vessels  containing 
one  litre  of  normal  saline  solution  (0.8  per  cent 
sodium  chloride) ;  the  alkali-albumin  in  one  litre 

1  Preparation  of  egg-albumin.  —  Thoroughly  mix  the  whites 
of  twelve  or  more  eggs  with  saturated  solution  of  magnesium 
sulphate  at  20°  C.  Filter  from  the  precipitated  globulin. 
Saturate  the  filtrate  at  20°  C.  with  sodium  sulphate.  Filter 
the  precipitated  albumin.  Press  in  filter  paper.  Dissolve  in 
water.  Dialyse  until  the  dialysate  is  free  from  sulphates. 
(Starke,  quoted  by  Haminarsten  :  Lehrbuch  der  physiologischen 
Chemie,  1897,  p.  372.)  Determine  the  albumin  in  a  measured 
quantity  of  the  solution,  as  follows. 

Quantitative  Estimation  of  Egg -albumin.  —  To  25  c.c.  of  the 
albuminous  liquid  add  an  equal  quantity  of  4  per  cent  sodium 
chloride  solution.  Neutralize  exactly.  Boil  5  c.c.  of  this  mix- 
ture in  a  test-tube.  To  the  boiling  liquid  add  one  drop  of  acetic 
acid  from  a  burette.  Filter  from  the  precipitated  proteid.  Pour 
the  filtrate  carefully  down  the  side  of  a  conical  glass  containing 
about  5  c.  c.  concentrated  nitric  acid,  so  that  the  lighter  liquid 
rests  on  the  heavier  acid.  If  the  surface  of  separation  remain 
clear,  all  the  albumin  in  the  5  c.c.  was  precipitated  by  adding 
to  the  boiling  liquid  one  drop  of  acetic  acid.  If  a  white  ring 
form,  albumin  is  still  present  (Heller's  test).  In  this  case  boil 
a  fresh  portion  (5  c.c),  add  two  drops  acetic  acid,  filter,  and 
test  the  filtrate.  Determine  in  this  way  how  much  acetic  acid 
must  be  added  to  each  5  c.c.  of  the  albuminous  liquid  to  pre- 
cipitate all  the  albumin  when  the  liquid  is  boiled.  Heat  25  c.c. 
of  the  remaining  portion  of  the  albuminous  liquid  in  a  water 
bath.  Add  slowly  with  constant  stirring  the  calculated  quan- 
tity of  acetic  acid.  Heat  ten  minutes  longer.  Filter  through 
weighed  paper.  Test  filtrate  once  more  for  albumin.  If  none  be 
present,  wash  with  water,  alcohol,  and  ether,  dry  at  40°,  weigh, 


FERMENTATION  249 

of  0.1  per  cent  sodium  carbonate  solution ;  and 
the  myosin  in  one  litre  of  5  per  cent  sodium 
chloride  solution. 

After   three  hours   determine   the  amount  ot 

subtract  the  weight  of  the  filter.  There  remains  the  weight  of 
the  albumin  in  25  c.c.  of  the  original  solution.1 

Preparation  of  Myosin.  —  Use  muscle  containing  little  blood 
(calf,  rabbit,  fowl,  frog).  Hash  the  muscle.  Wash  with  water 
until  the  washings  are  free  from  proteid.  Remove  excess  of 
wash  water  by  pressure.  Mix  with  enough  15  per  cent  solu- 
tion of  ammonium  chloride  to  cover  the  mass.  After  four  hours, 
filter  through  cloth  and  then  through  paper.  The  filtrate  should 
be  clear,  opalescent,  somewhat  thick.  Dialyse  in  running  water. 
As  the  neutral  salt  is  removed,  the  myosin  will  separate  in  fine 
flocks  (Danilewsky).  Redissolve  in  5  per  cent  sodium  chloride 
solution. 

Quantitative  Estimation  of  Myosin.  —Dialyse  25  c.c.  of  the 
saline  solution  of  myosin  until  the  dialysate  is  free  from  salt. 
Wash  the  precipitated  myosin  into  a  tall  narrow  beaker.  When 
the  myosin  has  settled,  decant  as  much  of  the  supernatant  liquid 
as  possible.  To  the  remainder  add  alcohol  in  such  proportion 
that  the  mixture  shall  contain  80  per  cent.  After  coagulation, 
filter  through  a  weighed  filter.  Wash  with  alcohol  and  ether. 
Dry  at  100°.     Weigh.     Subtract  the  weight  of  the  filter. 

Preparation  of  Alkali-albumin.  —  Warm  the  whites  of  twelve 
or  more  eggs  with  1  per  cent  sodium  hydrate  at  40°  C.  Filter. 
Neutralize  very  cautiously  with  hydrochloric  acid,  at  first  1  per 
cent,  later  0.1  per  cent.  The  alkali-albumin  will  be  precipi- 
tated. Allow  to  stand  several  hours.  Filter.  Boil  the  filtrate. 
Filter  from  the  fresh  precipitate  and  add  residue  to  first  pre- 

1  Literature.  —  Ku'hne:  TJntersuchungen  liber  das  Protoplasma,  1864, 
p.  2.  Danilewsky  :  Zeitsehrift  fiir  physiologische  Chemie,  1881,  v.  p.  15S. 
Halliburton  :  Journal  of  Physiology,  1887,  viii,  p.  132.  Kuhne  and 
Chittenden  :  Zeitsehrift  fiir  Biologic,  18S9,  xxv,  p.  358. 


250  THE   INCOME  OF  ENERGY 

proteid  in  each  tube  and  state  the  per  cent  that 
has  passed  through  the  membrane. 

Diffusion  through  Living  Intestinal  "Wall.1  — 
Through  a  small  opening  in  the  linea  alba  of  a 
fasting  anaesthetized  cat2  draw  out  a  loop  near 
the  middle  of  the  small  intestine.  Eemove  the 
contents  by  careful  stroking.  Tie  double  liga- 
tures 0.5  cm.  apart  around  the  intestine  at  one 
end  of  the  loop  and  similar  ligatures  at  a  point 
30  cm.  from  the  first  pair.     With  a  hypodermic 

cipitate.1  Wash  with  water.  Redissolve  in  water  containing 
0.1  per  cent  sodium  hydrate. 

Quantitative  Estimation  of  A Hcali- albumin.  —  Neutralize  a 
measured  quantity  of  the  solution.  Separate  the  neutralization 
precipitate  upon  a  weighed  filter.  Wash  with  water,  alcohol, 
and  ether.     Dry  and  weigh. 

Preparation  of  Peptones.  —  The  separation  of  peptone  from 
the  albumoses2  with  which  it  is  obtained  in  the  tryptic  diges- 
tion of  proteids  is  so  difficult  that  it  should  not  be  attempted 
in  these  experiments.  Add  commercial  peptone,  often  contain- 
ing albumoses  as  an  impurity,  to  a  small  quantity  of  boiling 
neutral  distilled  water.     Filter. 

Quantitative  Estimation  of  Peptone.  —  To  10  c.c.  of  the  liquid 
add  alcohol  in  such  proportion  that  the  mixture  shall  contain 
80  per  cent.  Filter  through  weighed  filter  paper.  Dry  at 
40°  C.  Weigh.  [This  method  is  not  exact,  but  is  to  be  pre- 
ferred for  the  purpose  in  hand.] 

1  Voit  and  Bauer  :  Zeitschrift  fiir  Biologie,  1869,  v,  p.  562. 

2  These  and  subsequent  operations  will  be  done  by  an  in- 
structor assisted  by  a  committee  of  the  class. 

1  Hawk  and  Oies  :  American  Journal  of  Physiology,  1902,  vii,  p.  4C0. 

2  Kuhne  :  Zeitsclirift  fiir  Biologic,,  1892,  xxix,  p.  1. 


FERMENTATION  251 

needle  attached  to  a  burette  inject  into  the 
loop  sufficient  egg-albumin  solution  to  distend  it 
slightly.  Measure  the  volume  of  the  solution 
injected.  The  content  of  this  solution  was  found 
in  the  course  of  the  experiment  on  diffusion 
through  dead  membranes  (page  245). 

Eeplace  the  loop  in  the  abdomen.  At  some 
distance  from  this  loop  prepare  a  control  loop 
with  double  ligatures  in  the  same  way,  but  leave 
the  control  loop  empty.  Sew  up  the  abdominal 
wound. 

After  three  hours,  kill  the  animal  (best  by 
puncture  of  the  spinal  bulb).  Eemove  the  loops 
by  cutting  between  the  double  ligatures.  Eapidly 
wash  the  outer  surface  with  water,  dry  the  sur- 
face with  filter  paper,  open  the  loops,  measure 
the  volume  of  the  contents,  wash  the  inner  sur- 
face, add  the  washings  to  the  contents,  and 
estimate  the  proteid  in  a  measured  portion. 

Perform  a  similar  experiment  with  solutions  of 
(2)  myosin,  (3)  alkali-albumin,  and  (4)  peptone. 

Compare  the  results  of  absorption  of  proteids 
through  the  living  intestinal  wall  with  absorp- 
tion through  dead  membranes.  It  will  appear 
that  the  living  cells  of  the  intestinal  wall  modify 
absorption  so  that  it  does  not  follow  the  law  of 
diffusion  through  dead  membrane. 

It  is  also  evident    that  egg-albumin,  myosin, 


252  THE   INCOME   OF   ENERGY 

alkali-albumin,  and  peptone  may  be  absorbed 
unchanged.  Indeed,  the  absorption  of  alkali- 
albumin  is  almost  or  quite  as  complete  as  that 
of  peptone.  The  conversion  of  proteids  to 
peptones  is  advantageous  but  not  essential  to 
absorption. 

Absorption  Velocity  Compared  with  Diffusion 
Velocity.1  —  Prepare  a  cat  as  in  Experiment  2. 
Fill  one  intestinal  loop  with  a  measured  quantity 
of  5  per  cent  dextrose  solution,  the  other  with 
0.25  per  cent  solution  of  sodium  sulphate.  After 
one  hour  kill  the  animal,  measure  the  liquid  re- 
maining in  the  two  loops  and  estimate  its  content 
in  dextrose  and  sodium  sulphate  respectively.2 

The  dextrose  solution  will  be  found  to  have 
been  largely  or  completely  absorbed,  while  rela- 

1  Rohmann:  Archiv  fur  die  gesammte  Physiologie,  1887, 
xii,  p.  456. 

2  The  quantitative  estimation  of  dextrose  is  described  in 
"Experiments  for  Students  in  the  Harvard  Medical  School," 
third  edition,  p.   38. 

Quantitative  Estimation  of  Sodium  Sulphate.  —  Boil  the  solu- 
tion, make  the  reaction  acid  with  a  few  drops  of  hydrochloric 
acid,  add  hot  solution  of  barium  chloride  in  slight  excess  (until 
barium  sulphate  ceases  to  be  precipitated).  Boil  a  few  minutes. 
Wait  for  the  precipitate  to  settle.  Decant  the  clear  liquid 
through  a  filter,  the  ash  of  which  is  of  known  weight.  Boil  the 
precipitate  in  the  beaker  repeatedly  with  water.  Place  the  pre- 
cipitate on  the  filter.  Wash  with  boiling  water.  Dry.  Heat  to 
redness  in  a  weighed  crucible.  Weigh  when  cold.  (The  atomic 
weights  are:  barium,  137.4;  sulphur,  32.06;  oxygen,  16.) 


FERMENTATION  253 

tively  little  of  the  sodium  sulphate  will  have 
left  the  intestine.  Yet  sodium  sulphate  is  some- 
what more  diffusible  than  dextrose.1 

Assimilable  Proteids.  —  With  a  catheter  re- 
move the  urine  from  the  bladder  of  an  anaesthe- 
tized female  cat,  and  apply  Heller's  test  for 
albumin  (page  248).  Albumin  should  be  absent. 
Slowly  inject  into  the  jugular  vein  25  c.c.  of 
solution  of  alkali-albumin  (page  249)  at  the  tem- 
perature of  the  body.  Test  the  urine  for  albumin 
twice,  at  intervals  of  half  an  hour. 

No  albumin  will  be  found.  The  alkali- albumin 
has  not  been  removed  from  the  blood  by  the 
kidneys. 

Non- Assimilable  Proteids.  —  Perform  a  similar 
experiment  on  another  cat,  injecting  solution  of 
egg-albumin  instead  of  alkali-albumin. 

Albumin  will  be  found  in  the  urine.  Egg- 
albumin,  present  in  the  blood,  is  at  once  re- 
moved by  the  kidneys.  It  cannot  be  used  unless 
changed  ("digested")  in  the  intestine.2  Albu- 
moses  and  peptones  are  also  non-assimilable ; 
they  produce  a  dangerous  fall  in  blood-pressure. 

1  Compare  Hoffmann:  Eckhard's  Beitrage  zur  Anatomie 
und  Physiologie,   1860,  ii,  p.  65. 

2  Munk,  J.,  and  M.  Lewandowsky  (Archiv  fur  Physiologie, 
1899,  Supplement,  pp.  73-88)  find  the  non-assimilable  proteids 
of  Neumeister  (not  including  albumoses  and  peptones)  may  be 
assimilated  if  injected  very  slowly  into  the  blood. 


254         THE  INCOME  OF  ENERGY 

Alimentary  Albuminuria.  —  Test  the  urine  of  a 
human  subject  for  albumin  at  half-hour  intervals. 
After  the  first  test  let  the  subject  swallow  the 
whites  of  six  raw  eggs. 

Albumin  will  probably  be  found.  In  many 
subjects  a  portion  of  any  unusual  quantity  of 
egg-albumin  may  be  absorbed  unchanged  into  the 
blood,  whence  it  is  removed  by  the  kidneys. 

Albumose  and  Peptone  not  ordinarily  Present 
in  the  Blood  or  Urine.  —  Dissolve  as  completely 
as  possible  ten  grams  of  commercial  peptone, 
which  contains  albumose  as  an  impurity,  in  a 
small  quantity  of  water.  Boil.  Filter.  Measure 
the  filtrate. 

Through  a  small  opening  in  the  linea  alba  of  a 
fasting  anaesthetized  cat  draw  out  a  loop  near  the 
middle  of  the  small  intestine.  Kemove  the  con- 
tents by  careful  stroking.  Tie  double  ligatures 
0.5  cm.  apart  around  the  intestine  at  one  end  of 
the  loop  and  similar  ligatures  at  a  point  30  cm. 
from  the  first  pair.  With  a  hypodermic  needle 
inject  into  the  loop  sufficient  peptone  solution  to 
distend  it  slightly.  Measure  the  amount  injected. 
Replace  the  loop  in  the  abdomen  and  close  the 
wound.  Keep  the  animal  in  a  cage  arranged  to 
collect  voided  urine. 

After  two  hours,  withdraw  the  urine  from  the 
bladder  and  add  it  to  any  that  may  have  been 
spontaneously  voided. 


FERMENTATION  255 

Bleed  the  animal  from  the  carotid  artery,  re- 
ceiving the  blood  into  an  equal  volume  of  satu- 
rated solution  of  ammonium  sulphate,  to  prevent 
coagulation.  Kemove  the  intestinal  loop  by  cut- 
ting between  the  double  ligatures.  Measure  the 
liquid  remaining  in  the  intestine.  It  will  be 
found  that  most  of  the  peptone  has  disappeared. 
Test    the    blood    and    the   urine   for    peptone 1 

1  Recognition  of  Peptone  in  Blood.  —  To  the  blood  already- 
mixed  with  an  equal  volume  of  ammonium  sulphate  solution 
add  crystals  of  ammonium  sulphate  to  saturation.  Filter  from 
the  precipitated  proteids.  To  the  clear  filtrate  apply  the  biuret 
test  for  peptone. 

Biuret  reaction.  —  To  the  saturated  ammonium  sulphate 
filtrate  add  half  its  volume  of  saturated  solution  of  potassium 
hydrate.  Shake  the  dense  precipitate.  Allow  the  tube  to 
stand  two  or  three  minutes  until  the  heat  developed  by  the 
chemical  action  passes  off.  Add  a  drop  of  very  dilute  solution 
of  cupric  sulphate.  The  fluid,  dense  white  from  the  precipitated 
salts,  assumes  a  pale  blue  color,  due  to  the  solution  of  hydrated 
cupric  oxide  in  the  ammonia  generated.  The  same  quantity  of 
saturated  potassium  hydrate  as  before  is  now  allowed  to  flow 
down  the  tube,  and  to  form  a  layer  at  the  bottom.  If  peptone 
is  present  a  rose  red  ring  is  formed  at  the  junction  of  the  two 
layers.  The  contrast  of  the  red  ring  with  the  pale  blue  above 
it  renders  the  test  very  delicate  (Neumeister's  method  modified 
by  Shore  :  Journal  of  Physiology,  1890,  xi,  pp.  532-534). 

Recognition  of  Peptone  in  Urine.  —  Remove  the  coloring 
matter  by  (1)  adding  solid  lead  acetate  and  filtering  from  the 
heavy  precipitate  ;  (2)  adding  to  the  filtrate  ammonium  sul- 
phate, and  filtering  from  the  copious  precipitate  of  lead  sulphate  ; 
(3)  saturating  the  filtrate  with  crystals  of  ammonium  sulphate 
and  filtering  from  the  additional  precipitate.     On  filtration  the 


256         THE  INCOME  OF  ENERGY 

with  the  biuret  reaction.  No  peptone  will  be 
found.1 

An  examination  of  the  lymph  would  show 
that  it  also  contains  no  peptone.  Apparently 
the  peptone  absorbed  from  the  intestinal  loop  is 
changed  in  its  passage  through  the  intestinal 
wall.  This  conclusion  is  made  secure  by  the  ex- 
periments of  Salvioli,2  who  removed  the  jejunum 
of  the  dog  or  rabbit,  tied  a  cannula  in  the  mesen- 
teric artery  and  vein,  and  established  through 
these  vessels  an  artificial  circulation  of  defibri- 
nated  blood  diluted  with  isotonic  saline  solution. 
One  gram  of  peptone  was  dissolved  in  10  c.c.  of 
normal  saline  solution  and  placed  in  the  intes- 
tine, and  the  artificial  circulation  maintained  four 
hours.  The  peptone  disappeared  from  the  intes- 
tine, but  none  could  be  found  in  the  blood. 

Albumose  and  Peptone  changed  in  their  Passage 
through  the  Intestinal  "Wall.  — -  Kill  a  fairly  large 
anaesthetized  rabbit  by  bleeding.     Beat  the  blood 

solution  is  free  from  lead,  but  usually  still  contains  a  trace  of 
yellow  pigment.  Apply  the  biuret  reaction  as  above.  If  the 
urine  requires  to  be  concentrated,  it  is  better  to  evaporate  the 
final  ammonium  sulphate  filtrate,  as  boiling  the  urine  at  first 
deepens  the  color.     (Neumeister  and  Shore,  lot.  cit.) 

1  Neumeister:  Zeitschrift  fur  Biologie,  1888,  xxiv,  pp. 
278-279. 

2  Salvioli  :  Archiv  fur  Physiologic,  1880,  Supplemental 
volume,  p.   112. 


FERMENTATION  257 

until  all  the  fibrin  separates.  Filter  through 
gauze  into  a  cylinder  holding  100  c.c.  To  the 
30  c.c.  defibrinated  blood  add  30  c.c.  sodium 
chloride  solution  (0.5  per  cent)  containing  0.6 
gram  salt-free  peptone.  The  mixture  will  thus 
contain  1.0  per  cent  of  peptone.  Eeserve  5  c.c. 
of  the  mixture.  Place  the  rest  in  a  half-litre 
flask,  provided  with  a  stopper  pierced  by  two 
glass  tubes,  one  reaching  to  near  the  bottom 
of  the  flask,  the  other  ending  just  beneath  the 
stopper  so  that  air  may  be  drawn  through  the 
blood-peptone  solution  by  an  aspirator.  Place 
the  flask  in  a  beaker  with  a  heavy  iron  ring 
around  the  neck  to  prevent  the  flask  being  driven 
upward,  fill  the  beaker  with  water  at  40°  C.  and 
place  it  in  a  water  bath  also  at  40°. 

Separate  the  intestine  carefully  from  the  mes- 
entery and  especially  the  pancreas.  Slit  the 
intestine  from  the  pylorus  to  the  ilio-csecal  valve 
with  scissors,  cut  it  into  several  pieces,  wash  it 
in  a  large  water-bath  filled  with  0.5  per  cent 
sodium  chloride  solution  at  40°  C.  Eepeat  the 
washing  in  a  second  and  a  third  bath.  Cut  the 
intestine  into  finger-lengths.  Collect  the  pieces 
on  a  porcelain  sieve,  wash  them  with  1  per  cent 
peptone  solution,  and  then  place  them  in  the 
blood-peptone  solution.  Draw  air  through  the 
solution,  with  every  possible  care  against  foam- 

17 


258         THE  INCOME  OF  ENERGY 

ing.  These  several  operations,  beginning  with 
the  bleeding  of  the  rabbit,  should  take  not  more 
than  fifteen  minutes. 

After  two  hours  interrupt  the  experiment, 
pour  the  solution  through  a  sieve,  stir  into  the 
filtrate  solid  ammonium  sulphate  to  saturation, 
filter  off  about  10  c.c.,  add  to  the  water-clear  fil- 
trate an  equal  volume  of  absolute  sodium  hydrate 
(70  per  cent),  stir  thoroughly  with  a  glass  rod, 
and  let  the  precipitated  sodium  sulphate  settle. 

Add  to  the  clear  liquid  drop  hy  drop  2  per 
cent  cupric  sulphate  solution.  No  biuret  reaction 
will  be  obtained,  but  the  liquid  will  show  at  once 
a  pure  blue  color. 

Eepeat  the  test,  with  the  same  quantitative 
relations,  upon  the  reserved  5  c.c.  of  the  blood- 
peptone  solution  :  a  purple  color  will  be  obtained. 

Hence  the  not  inconsiderable  quantity  of  pep- 
tone in  the  blood  covering  the  pieces  of  intestine 
lias  disappeared. 

Rub  the  pieces  of  intestine  with  sand  to  a 
pulp,  boil  with  as  little  water  as  possible,  saturate 
with  ammonium  sulphate,  and  test  as  before. 

No  biuret  reaction  will  be  obtained.  Hence 
the  peptone  which  disappeared  from  the  blood- 
peptone  solution  is  not  stored  in  the  intestine.1 

1  NbUMBISTER  :  Zcitschrift  fur  Biologie,  1890,  xxvii,  pp.  324- 
327. 


FERMENTATION  259 

Cohnheim 1  attempted  to  find  in  the  intestinal 
wall  the  peptone  which  disappears  from  the 
intestine  without  enterinG:  the  intestinal  blood 
and  lymph.  His  failure  led  him  to  the  dis- 
covery of  a  new  ferment  Erepsin  (epziTrw,  I  de- 
stroy), the  action  of  which  is  to  split  peptone  into 
crystallizable  substances.  This  ferment,  which  is 
found  in  many  tissues,  was  isolated  by  fractional 
precipitation  with  ammonium  sulphate.  Two 
parts  of  intestinal  extract  were  mixed  with  three 
parts  of  concentrated  ammonium  sulphate.  The 
resulting  thick  precipitate,  consisting  largely  of 
proteid  was  dialyzed,  and  the  erepsin  found  in 
the  dialysate. 

The  disappearance  of  peptone  from  the  intes- 
tine is  probably  therefore  not  to  be  explained  by 
the  assimilation  of  the  peptone  or  its  reconver- 
sion into  other  forms  of  proteid,  but  by  the  split- 
ting of  the  peptone  through  the  action  of  the 
ferment  erepsin. 

Absorption  of  Fats,  Fat  Acids,  and  Soaps2 

Absorption  of  Fat.  —  1.  Place  a  few  drops  of 
neutral  olive  oil  in  the  pharynx  of  a  frog  that 

1  Cohnheim:  Zeitschrift  fur  physiologische  Chemie,  1901, 
xxxiii,  pp.  451-465. 

2  Will  :  Archiv  far  die  gesammte  Physiologie,  1879,  xx, 
pp.  255-262.  These  experiments  are  best  performed  upon 
summer  frogs,  i.  e.  not  during  the  normal  period  of  hibernation. 


260  THE    INCOME    OF   ENERGY 

has  fasted  at  least  fourteen  days.  After  about 
twenty-four  hours,  remove  the  intestine  and  im- 
merse it  from  thirty  to  forty  minutes  in  0.25  per 
cent  osmic  acid  solution.1 

Slice  the  epithelial  layer  from  its  base.  Tease 
on  a  glass  slide  and  examine  under  the  micro- 
scope. 

Particles  of  fat  stained  deep-brown  by  the  osmic 
acid  will  be  found  in  the  epithelial  cells. 

In  a  "  control "  frog  that  has  fasted  fourteen 
days,  show  that  the  intestinal  epithelium  is  free 
from  fat. 

2.  Open  the  stomach  of  a  frog  the  brain  and 
spinal  cord  of  which  have  been  destroyed.  Tie 
a  glass  cannula  in  the  pylorus.  Tie  a  ligature 
around  the  lower  end  of  the  intestine.  Eemove 
the  intestine.  Place  about  1  c.c.  normal  saline 
solution  in  a  test-tube.  Hang  the  intestine  in 
the  test-tube  by  passing  the  cannula  through 
the  cork.  Place  a  little  neutral  olive  oil  in  the 
intestine.  After  about  twenty-four  hours  stain 
the  epithelium  with  osmic  acid  and  examine  as 
before. 

Drops  of  fat  will  be  found  in  the  cells,  but  the 

1  Preparation  of  Osmic  Acid  Solution.  —  The  glass  capsule 
containing  a  known  quantity  of  osmic  acid  is  placed  in  a  bottle 
and  enough  water  is  then  added  to  make  the  required  solution. 
The  capsule  is  then  broken.  [The  vapor  of  osmic  acid  is  very 
irritating.] 


FERMENTATION  261 

quantity  absorbed  will  be  less  than  in  the  living 
animal. 

3.  Kepeat  Experiment  2,  using  an  emulsion  of 
commercial  olive  oil  and  0.25  percent  solution  of 
sodium  carbonate. 

Absorption  will  be  increased  by  the  giving  of 
the  fat  in  an  emulsion. 

Absorption  of  Fat  Acids.  —  Place  in  the  pharynx 
of  a  frog  a  pill  of  pure  palmitic  acid  made  with  a 
few  drops  of  glycerine.  After  about  twenty-four 
hours  examine  as  before. 

Numerous  drops  of  fat  will  be  found  in  the  in- 
testinal epithelium.  These  globules  are  not  free 
fat  acid  absorbed  as  emulsion,  for  miscrocopic 
examination  of  the  contents  of  the  intestine 
shows  no  emulsion.  Moreover,  palmitic  acid 
must  be  liquid  to  be  emulsified,  and  as  its  melt- 
ing-point is  62°  C.  it  could  not  melt  in  the 
intestine  of  a  cold-blooded  animal  at  room  tem- 
perature. 

Absorption  of  Fat  Acid  as  a  Soap.1  —  Feed  a 
frog  with  palmitin  soap  containing  a  few  drops  of 
glycerine.  After  about  twenty-four  hours  exam- 
ine the  intestine  for  fat,  as  before. 

1  Preparation  of  Palmitin  Soap.  —  Dissolve  ten  grams  pure 
palmitic  acid  in  hot  alcohol.  Add  enough  5  per  cent  potassium 
hydrate  to  combine  with  the  fat  acid.  Drive  off  the  alcohol 
by  heating  on  a  water-bath.  Dilute  with  water  and  add  a  few 
drops  of  glycerine. 


262  THE    INCOME    OF   ENERGY 

Fat  globules  will  be  found  in  the  epithelial 
cells. 

Lymph 

Permeability  of  Vessel  Wall  in  Inflammation. 
—  1.  In  a  curarized  frog  whose  brain  has  been 
destroyed  by  pithing  spread  the  mesentery  over 
the  glass  plate  of  the  mesentery  board,  and  ob- 
serve the  capillary  circulation  under  the  micro- 
scope. Note  the  following  changes.  Dilatation 
of  the  arteries,  veins,  and  capillaries,  in  the  order 
named.  With  the  dilatation  an  increase  in  the 
speed  of  the  blood-stream,  most  noticeable  in 
the  arteries.  After  half  an  hour  to  an  hour  the 
acceleration  gives  place  to  slowing.  All  the 
vessels  are  now  dilated,  many  capillaries  are 
plainly  visible  that  could  hardly  be  made  out  in 
the  normal  state,  the  pulsation  in  the  arteries 
is  uncommonly  strong  down  to  their  smallest 
branches,  yet  the  circulation  is  everywhere  slug- 
gish. In  consequence  of  the  slow  blood-stream, 
the  capillaries  become  crowded  with  corpuscles, 
so  that  they  appear  redder  and  more  volumi- 
nous than  normal,  yet  their  cross-section  is  only 
slightly  increased.  In  the  veins  the  normally 
almost  clear  plasma  next  the  wall  fills  gradually 
with  leucocytes.  The  white  corpuscles  pass 
through  the   walls  of  the   veins   and  capillaries. 


FERMENTATION  263 

Eed  corpuscles  escape  from  the  capillaries. 
Hand  in  hand  with  the  extravasation  of  cor- 
puscles, there  is  an  increased  transudation  of 
lymph.  The  tissue  swells  with  lymph,  which 
soon  exudes  upon  the  free  surface  of  the  mes- 
entery, where  it  clots.  The  surface  is  then 
covered  with  a  fibrinous  membrane,  crowded 
with  white  corpuscles,  and  containing  also  some 
red  corpuscles.1 

2.  Place  on  the  frog's  tongue  a  small  drop  of 
croton  oil  mixed  with  fifty  times  its  volume  of 
olive  oil.  After  thirty  seconds  wipe  off  the 
croton  oil.  Observe  the  inflammatory  process 
under  the  microscope. 

3.  Place  a  rubber  band  around  the  base  of  a 
white  rabbit-ear  and  thus  interrupt  the  venous 
flow.  Hold  the  tip  of  the  ear  in  warm  water 
until  it  has  a  temperature  of  about  44°  0. 
Take  the  ear  from  the  water  and  remove  the 
band. 

•  Note  the  rosy  swelling  (oedema  with  slight 
extravasation  of  blood-corpuscles)  in  the  in- 
flamed area.2 

1  Cohnheim:  Allgemeine  Pathologie,  1882,  i,  pp.  237-241. 

2  Id. :  Loc.  cit.,  pp.  244-245. 


264  THE    INCOME    OF   ENERGY 

II   BLOOD 
Specific  Gravity 

Drawing  the  Blood.  — Wash  the  lobe  of  the  ear 
with  a  bit  of  absorbent  cotton  dipped  in  clean 
water.1  Bub  the  lobe  dry  with  another  piece 
of  cotton.  Pass  a  three-sided  surgical  needle 
through  a  Bunsen  name.  (Do  not  heat  the 
needle  red  or  the  temper  will  be  drawn  and  the 
sharpness  lost.)  Stretch  the  skin  of  the  lobe 
between  the  fingers  of  the  left  hand.  Make  a 
quick  puncture  one -eighth  inch  deep  in  the  edge 
of  the  lobe.  Press  gently  to  start  the  flow.  The 
blood  must  now  flow  freely.  On  no  account  use 
blood  squeezed  out. 

Determination  of  Specific  Gravity.2  —  Fill  a 
small  beaker  half  full  of  a  mixture  of  benzol  and 
chloroform  of  a  specific  gravity  of  about  1059. 
Let  a  drop  of  the  blood  fall  into  this  mixture. 
The  drop  will  remain  spherical,  for  blood  does 
not  mix  with  benzol  and  chloroform.  If  the 
drop  sinks,  add  chloroform  drop  by  drop,  mean- 
while stirring  the  mixture  with  a  glass  rod,  until 

1  Subjects  who  are  "  bleeders"  are  not  to  be  used  for  this 
observation . 

2  Roy:  Journal  of  Physiology,  1884,  v,  p.  ix.  Ham- 
MEU8CHLAG,  A.  :  Wiener  klinische  Wochensehrift,  1890,  iii, 
p.  1018. 


BLOOD  265 

the  drop  neither  rises  to  the  surface  nor  sinks 
to  the  bottom  but  swims  with  the  mixture.  If 
the  drop  rests  upon  the  surface,  add  benzol  in 
a  similar  manner.  When  the  drop  neither  sinks 
nor  floats,  its  specific  gravity  must  be  that  of  the 
benzol-chloroform  mixture.  Pour  the  mixture 
into  a  glass  cylinder,  through  a  piece  of  linen  to 
hold  back  the  blood-drop,  and  take  the  specific 
gravity  of  the  benzol-chloroform  with  an  areom- 
eter. The  result  is  also  the  specific  gravity  of 
the  blood. 

The  values  obtained  are  slightly  too  low.  The 
error  is  one  unit  in  the  third  decimal  place. 

Determine  the  specific  gravity  of  the  blood 
under  the  following  conditions.  Record  the  re- 
sults in  the  laboratory  note-book.  Hand  to  the 
instructor  a  copy  of  your  observations  written  in 
ink  upon  a  laboratory  blank.  The  material  col- 
lected by  the  class  will  be  analyzed  statistically 
by  a  committee  and  a  report  made. 

1.  The  specific  gravity  of  the  blood  in  a  healthy 
man. 

2.  In  the  same  man  half  an  hour  after  drink- 
ing 750  c.c.  of  water. 

3.  In  the  same  man  one  hour  after  drinking 
750  c.c.  of  water. 

4.  In  the  same  man  after  profuse  sweating. 
Note  any  feeling  of  thirst. 


266  THE   INCOME   OF  ENERGY 

5.    In  a  healthy  woman. 

Haromerschlag  found  the  specific  gravity  in 
chlorosis  and  nephritis  diminished  as  the  haemo- 
globin diminished.  No  relation  was  observed 
between  the  appearance  of  oedema  and  a  reduc- 
tion in  the  specific  gravity. 

Counting  the  Corpuscles 

Counting  the  Red  Corpuscles.  —  See  that  the 
pipettes  of  the  Thoma-Zeiss  apparatus  are  per- 
fectly clean  and  dry.  Open  the  bottle  contain- 
ing Gower's  solution  (sodium  sulphate,  7.3  grams  ; 
acetic  acid,  20  c.c. ;  water,  125  c.c).  Prick  the 
ear  as  directed  on  page  264.  In  a  large  drop 
which  has  collected  without  pressure  put  the 
point  of  the  smaller  Thoma-Zeiss  pipette  (  "  red 
counter  "  ).  Fill  the  pipette  to  the  mark  0.5  by 
careful  suction.  Should  the  mark  be  passed, 
lower  the  column  to  the  mark  by  touching  the 
point  of  the  pipette  to  filter  paper.  When  the 
mark  is  reached,  clean  the  outside  of  the  pipette, 
dip  the  end  in  Gower's  diluent  solution,  and 
draw  the  liquid  very  carefully  up  to  the  mark 
101.  (Should  the  liquid  pass  the  mark,  the 
pipette  must  be  cleaned  and  dried  and  the  whole 
process  repeated.)  Close  the  ends  of  the  pipette 
with   the   fingers,   and  shake   it  gently   for   one 


BLOOD  267 

minute  in  order  to  mix  the  blood  thoroughly 
with  the  diluent.  The  blood  will  now  be  diluted 
200  times  its  volume. 

Eemove  the  rubber  tube  from  the  pipette. 
Blow  out  the  unmixed  solution  in  the  capillary 
tube,  between  the  point  and  the  bulb,  and  several 
drops  of  the  mixture  in  the  bulb.  Wipe  off  the 
end  of  the  pipette.  Touch  it  to  the  ruled  disc. 
Let  a  very  small  drop  flow  out.  Place  the  cover 
glass  on  the  drop.  The  flattened  drop  should 
almost  cover  the  glass.  If  it  spread  into  the 
moat,  clean  the  disc  and  use  a  second,  smaller 
drop.  If  Newton's  color-rings  cannot  be  seen 
between  the  cover-glass  and  the  disc  by  placing 
the  eyes  near  the  level  of  the  cover-glass,  another 
preparation  must  be  made,  with  cleaner  disc  and 
cover-glass. 

Use  Leitz  No.  5  or  Zeiss  D  objective.  Bring 
the  drop  into  focus  and  then,  using  the  microm- 
eter screw,  find  the  ruled  field. 

On  the  central  portion  of  the  disc  1  square 
millimetre  has  been  ruled  into  400  squares,  each 
square  having  therefore  an  area  of  ^-j-g-  square 
millimetre.  Each  16  small  squares  are  sur- 
rounded by  double  lines,  thus  forming  a  "  large 
square."  In  the  Zappert-Ewing  slide,  the  cen- 
tral square  of  1  mm.  is  surrounded  by  eight  other 
squares  of  1  mm.  each,  and  the  central  ruling  is 


268        THE  INCOME  OF  ENERGY 

extended  through  the  surrounding  squares,  which 
are  intersected  by  lines  ^  mm.  apart.  Count  the 
number  of  corpuscles,  square  by  square,  in  200 
small  squares.  Corpuscles  touching  the  north 
and  south  lines  of  each  area  are  to  be  counted 
in,  those  touching  the  east  and  west  lines  are  to 
be  omitted  from  the  count. 

Each  square  has  an  area  of  ^^  square  milli- 
metre. The  thickness  of  the  layer  of  blood,  i.  e. 
the  distance  from  the  ruled  disc  to  the  cover- 
glass,  is  0.1  mm.  The  volume  of  the  space  above 
each  square,  therefore,  is  4  oVo  CUDic  millimetre. 
As  the  blood  is  diluted  200  times  its  volume,  and 
the  number  of  squares  counted  is  200,  the  total 
number  of  corpuscles  in  a  cubic  millimetre  is 
x  X  200  X  4000 
200 
x  being  the  total  number  of  corpuscles  counted. 
In  short,  to  obtain  the  number  of  corpuscles  in  a 
cubic  millimetre,  multiply  by  4000  the  number 
counted  in  200  squares.  Clean  the  pipette  as 
soon  as  the  counting  is  done. 

Cleaning  the  Pipette. —  Draw  clean  Gower's 
solution  through  the  pipette,  then  alcohol,  and 
finally  ether.  Dry  the  pipette  by  sucking  (not 
blowing)  air  through  it.1 

1  Do  not  use  alcohol  and  ether  in  cleaning  the  disk.  Pi- 
pettes left  dirty  will  be  cleaned  at  the  student's  expense,  or, 
where  necessary,  a  new;one  purchased. 


BLOOD  269 

Control  Counting. —  Count  the  red  corpuscles 
in  a  second  drop.  If  the  result  differ  greatly 
from  that  of  the  first  count,  the  corpuscles  in  a 
third  drop  must  be  counted. 

Counting  the  White  Corpuscles. —  Have  ready 
a  diluting  solution  of  glacial  acetic  acid  (one- 
third  of  one  per  cent).  This  solution  will  make 
the  red  cells  invisible.  Obtain  a  very  large  drop 
of  blood.  By  very  gentle  suction  fill  the  large 
Thoma-Zeiss  pipette  to  the  point  0.5.  Keep 
the  pipette  nearly  horizontal,  both  in  obtain- 
ing the  drop  and  in  drawing  in  the  diluting  solu- 
tion ;  the  bottle  should  be  tilted.  Count  the 
white  corpuscles  in  the  entire  ruled  disc.  Eepeat 
with  a  second  drop.  Calculate  the  number  of 
white  corpuscles  in  a  cubic  millimetre. 

Estimation  of  Haemoglobin 

Oxygen  Capacity  of  the  Blood  ;  the  Colorimetric 
Determination  of  Haemoglobin.  1 —  Haldane  and 
Smith 2  have  shown  that  "  the  coloring  power  of 
the  blood  of  different  mammals  varies  in  exact 

1  Haldane  :  Journal  of  Physiology,  1901,  xxvi,  pp.  497- 
504.  This  experiment  should  be  substituted  for  that  given  in 
"Experiments  for  Students  in  the  Harvard  Medical  School," 
third  edition,  pp.  100,  101. 

2  Haldane  and  Smith  :  Journal  of  Physiology,  1900,  xxv, 
pp.  331-343. 


270         THE  INCOME  OF  ENERGY 

proportion  to  its  oxygen  capacity.  The  latter 
can  be  easily  and  accurately  determined  by 
means  of  the  ferricyanide  method.1  Thus  blood 
of  a  certain  oxygen  capacity  has  also  a  certain 
coloring  power ;  and  it  is  possible  to  standardize 
the  coloring  power  in  terms  of  the  oxygen  capa- 
city. We  can  therefore  make  the  unit  of  volume 
the  basis  of  our  definition  of  the  unit  of  color- 
ing power  employed  in  haemoglobin  estimations. 
Since,  however,  oxy-lnemoglobin  is  not  stable, 
I  have  adopted  as  a  standard  a  dilute  solution 
of  blood  of  known  oxygen  capacity  saturated 
with  coal  gas.2  This  solution  is  sealed  up  in 
a  narrow  test-tube  after  all  the  contained  air 
has  been  displaced  by  coal  gas,  and  when  thus 
completely  sealed  is  permanent." 

The  standard  solution  for  the  ruemoglobin- 
ometer  is  a  one  per  cent  solution,  saturated  with 
coal  gas,  of  ox  or  sheep's  blood  of  the  average 
oxygen  capacity  of  the  blood  of  normal  adult 
males,  found  to  be  18.5  per  cent.  If  it  be  borne 
in  mind  that  100  per  cent  on  the  hsemoglobin- 
ometer  scale  corresponds  to  an  oxygen  capacity 

1  In  this  method  the  oxygen  is  displaced  from  laked  blood 
by  ferricyanide  of  potassium,  and  the  resultant  gas  measured. 
HALDANB:  Journal  of  Physiology,  1900,  xxv,  pp.  295-302. 

2  Coal  gas  contains  carbon  monoxide  as  an  impurity,  and 
thus  converts  the  oxy-haemoglobin  to  CO-hsemoglobin. 


BLOOD  271 

of  18.5  per  cent,  it  is  of  course  easy  to  express 
the  results  in  terms  of  oxygen  capacity.  The 
exact  percentage  of  haemoglobin  corresponding  to 
18.5  per  cent  oxygen  capacity  is  still  uncertain. 
According  to  Hufner's  latest  results  it  would  be 
13.8  per  cent. 

In  using  the  haemoglobinometer,  place  15-20 
c.c.  water  in  the  graduated  tube,  for  dilution  of 
the  blood.  Draw  20  cb.  mm.  of  blood  into  the 
pipette,  with,  the  necessary  precautions.1  Gently 
blow  the  blood  out  of  the  pipette  on  to  the  sur- 
face of  the  water  in  the  graduated  tube.  Before 
mixing  the  blood  with  the  water  introduce  into 
the  free  part  of  the  tube  a  narrow  glass  tube  con- 
nected with  the  gas-tap,  turn  on  the  gas,  and 
push  the  gas-tube  down  to  near  the  level  of  the 
water,  so  that  the  air  may  be  instantly  displaced 
from  the  tube.  Avoid  any  loss  of  liquid.  If 
the  upper  part  of  the  tube,  or  the  liquid  itself, 
is  warmed  by  the  fingers  while  the  solution  is 
being  mixed  or  saturated  with  carbon  monoxide, 
a  little  liquid  is  apt  to  spurt  out.  This  can  be 
avoided  by  holding  the  tube  in  a  cloth.  With- 
draw the  gas-tube  while  the  gas  is  still  flowing. 
Close  the  top  of  the  graduated  tube  with  the 
finger  and  invert  the  tube  about  a  dozen  times, 

1  See  page  264  ;  remember  not  to  use  blood  squeezed  from 
the  ear. 


272  THE   INCOME   OF   ENERGY 

so  that  the  haemoglobin  is  thoroughly  saturated 
with  carbon  monoxide  and  the  full  pink  tint 
of  the  CO-haemoglobin  appears.  Then  add  water 
drop  by  drop  from  a  pipette  until  the  tint  in 
the  graduated  tube  equals  that  in  the  standard 
tube.  In  comparing  the  tints  of  the  two  tubes, 
it  is  best  to  hold  them  up  against  the  light  from 
the  sky.  The  precaution  must  always  be  taken 
of  repeatedly  transposing  the  tubes  from  side  to 
side  during  the  observations :  otherwise  very 
considerable  error  may  arise.  The  percentage 
is  read  off  on  the  tube  after  half  a  minute  has 
been  allowed  for  the  liquid  to  run  down.  An- 
other drop  is  now  added,  and  if  necessary  another, 
until  the  tints  again  appear  unequal.  Usually 
the  tints  will  appear  equal  for  two  or  possibly 
three  additions.  The  mean  of  the  readings  which 
gave  equality  is  taken  as  the  correct  result.  The 
results  in  successive  experiments  with  the  same 
blood  should  agree  within  one  per  cent  of  the 
mean. 

The  average  percentage  of  haemoglobin  in  the 
blood  of  women  is  11  per  cent,  and  in  the  blood 
of  children  13  per  cent  below  that  of  adult  men. 
In  calculating  the  proportion  of  haemoglobin  in 
the  blood  of  women  and  children  as  percentages 
of  the  average  normal  proportion,  it  is  evidently 
necessary  to  add   about   one-eighth   for   women 


BLOOD  273 

and  one-seventh  for  children  to  the  percentage 
found  by  the  haetnoglobinometer,  with  the  stand- 
ard solution  described  above. 

HEMORRHAGE   AND   EEGENERATION 

Determine  the  specific  gravity,  number  of  red 
and  white  corpuscles  per  millimetre,  and  per- 
centage of  haemoglobin  in  the  same  animal  under 
the  following  conditions :  Normal ;  two  hours 
after  a  profuse  haemorrhage ;  one  day,  three  days, 
and  five  days  after  the  haemorrhage.  Plot  all 
three  curves  upon  one  co-ordinate  system. 

Physical  Aspects  of  Coagulation 

Physical  Action  of  Salts  in  the  Coagulation  of 
Colloidal  Mixtures.  —  1.  Boil  egg-albumin  diluted 
with  about  eight  volumes  of  water.  The  colloid 
will  not  coagulate.  Add  crystals  of  magnesium 
sulphate  gradually.     Coagulation  will  take  place.1 

2.  Dip  a  thin  thread  of  silk  in  2  per  cent 
solution  of  calcium  chloride  and  lay  the  thread 
upon  a  glass  slide  beneath  a  cover-glass.  Allow 
boiled  solution  of  egg-white  (1  :  8)  to  run  under 
the  cover-glass.  Examine  the  process  of  coagu- 
lation under  a  magnification  of  about  500  diam- 

1  Hayciiaft  and  Duggan  :  British  Medical  Journal,  1890, 
p.  167. 

18 


274         THE  INCOME  OF  ENERGY 

eters.  The  fluid  at  first  is  free  from  visible 
particles.  Near  the  silk  thread  appears  a  fine 
cloud,  the  particles  in  which  grow  in  size  until 
they  form  spherules  having  a  maximum  diameter 
of  0.75  to  1/n.  They  are  now  seen  to  be  arranged 
in  patterns  forming  an  open  net  with  regular 
polygonal  meshes,  having  diagonals  as  long  as  6/x. 
The  threads  of  the  net  are  formed  of  contiguous 
spherules.  This  stage,  however,  is  not  one  of 
equilibrium  —  the  net  shrinks,  the  meshes  become 
smaller,  and  the  spherules  apparently  shift  their 
points  of  attachment  until,  in  place  of  being- 
bounded  by  threads  composed  of  several  spher- 
ules, the  image  has  the  appearance  of  the  typical 
fine  net  with  spherules  at  the  nodal  points  joined 
by  tiny  threads.  Whether  these  joining-threads 
or  bars  have  a  real  existence,  or  whether  they 
are  purely  optical  and  the  spherules  actually 
touch  one  another,  it  is  impossible  to  say  at 
present.  When  the  particles  are  large  enough 
to  be  clearly  visible  with  a  magnification  of  500 
diameters  they  do  not  show  Brownian  movement 
—  in  other  words  they  are  probably  already  in 
some  way  linked  to  one  another. 

The  following  explanation  of  these  phenomena 
may  be  given.  On  boiling  the  egg-albumin,  the 
heat  chemically  alters  the  dissolved  proteid  and 
produces    a   suspension    of    particles    having   an 


BLOOD  275 

average  diameter  commensurable  with  the  mean 
wave-length  of  light.1  Under  the  influence  of 
electrolytes  (the  salt  solution)  the  particles 
aggregate  to  larger  and  larger  masses.  When 
these  molecular  aggregates  attain  a  certain  size 
the  fluid  condition  is  no  longer  possible ;  this 
would  follow  immediately  from  Graham's  ob- 
servation that  actual  coagulation  is  preceded  by 
a  continuous  increase  in  the  viscosity  of  the  liquid. 
The  following  conditions  determine  this  generic 
action  of  salts  as  coagulants,  as  distinguished 
from  any  specific  chemical  action.  1.  The  point 
at  which  coagulation  appears  is  determined  by 
the  concentration  of  the  solid  in  the  colloidal  mix- 
ture, and  the  temperature,  molecular  concentra- 
tion (gram-molecules  per  litre),  and  nature  of 
the  electrolytes  present.  2.  The  concentration 
necessary  for  coagulation  is  lowered  by  a  rise  of 
temperature,  or  by  an  electrolyte.  3.  The  coagu- 
lative  energy  of  electrolytes  as  measured  by  the 
number  of  gram-equivalents  per  litre  necessary 
to  produce  coagulation  is  determined  almost 
solely  by  the  nature  of  the  metal  of  the  salt ; 
and  among  the  metals  themselves  it  is  deter- 
mined by  the  valency  of  the  metal.2 

1  Picton     and    Likder:    Transactions     of    the    Chemical 
Society,   1895,  lxvii,  p.  63. 

2  Haedy  :  Journal  of  Physiology,  1899,  xxiv,  pp.   181-183. 


276  THE    INCOME   OF   ENERGY 

Physical  Changes  in  Coagulation.  —  1 .  Clotting 
of  Plasma.  —  Wet  a  small  filter  with  cane-sugar 
solution  (0.5  per  cent).  Cut  a  frog's  ventricle 
across  near  the  base  so  that  0.5  c.c.  blood  shall  fall 
into  a  beaker  containing  an  equal  quantity  of  cane- 
sugar  solution.  Pour  the  mixture  on  the  filter. 
Eeceive  the  filtrate  on  a  watch-glass.  Note  the 
physical  changes  in  this  filtrate. 

2.  Fibrin  Threads.  —  Place  a  blood-drop  under 
a  cover-glass.  With  the  microscope  observe  the 
appearance  of  fibrin  threads. 

3.  Eeceive  1  c.c.  blood  into  0.5  c.c.  saturated 
solution  MgS04.  Note  (1)  absence  of  clotting, 
and  (2)  its  appearance  after  dilution. 

4.  Receive  0.5  c.c.  blood  in  a  watch-glass. 
Let  it  stand  twenty-four  hours.  Note  physical 
changes  during  the  first  ten  minutes  and  at 
end  of  period. 

Secretion 

Speed  of  Absorption  and  Secretion.  —  Place 
5  c.c.  of  thin  starch  paste  and  2  c.c.  concentrated 
nitric  acid  in  each  of  ten  test-tubes  and  mark 
them  2,  4,  6,  8,  10,  12,  14,  16,  18,  and  20 
minutes.  Let  one  of  each  pair  of  students  swal- 
low a  gelatine  capsule  containing  ten  grains  of 
potassium   iodide.1     Immediately  rinse  the  sub- 

1  The  subject  should  have  had  a  small,  early  breakfast. 


RESPIRATION  277 

ject's  mouth  until  the  wash  water  gives  no  blue 
color  (iodide  of  starch)  on  the  addition  of  potas- 
sium iodide  and  concentrated  nitric  acid  (to  set 
free  the  iodine).  Let  the  subject  chew  a  small 
piece  of  clean  black  rubber-tubing  to  increase 
the  secretion  of  saliva.  At  intervals  of  two 
minutes,  beginning  with  the  swallowing  of  the 
potassium  iodide,  empty  the  mouth  into  the  cor- 
responding test-tube,  at  once  rinse  the  mouth 
with  water,  and  begin  a  fresh  collection.1 

Note  the  moment  at  which  the  drug  appears 
in  the  saliva. 

RESPIRATION 
Chemistry  of  Kespiration 

Estimation  of  Oxygen,  Carbon  Dioxide,  and 
Water.2  —  Weigh  bottles  3,  4,  and   5  (4  and  5 

1  If  the  saliva  secreted  during  two  minutes  cannot  be  held 
in  the  mouth  with  comfort  and  without  loss  by  swallowing,  the 
mouth  may  be  emptied  into  a  freshly  washed  porcelain  dish, 
from  which  the  saliva  should  be  poured  into  the  proper  test- 
tube  at  the  end  of  each  two-minute  period. 

2  Apparatus.  —  Two  aspirator  bottles,  with  box.  A  wooden 
tray,  containing  a  jar  for  the  guinea-pig,  and  six  bottles,  viz. : 
Nos.  1  and  4,  filled  with  soda-lime,  to  absorb  carbonic  acid  ; 
N"os.  2,  3,  and  5,  filled  with  pumice  stone  soaked  in  sulphuric 
acid,  to  absorb  moisture  ;  No.  6,  a  Miiller  valve,  to  prevent  air 
being  forced  back  through  the  series  of  bottles  by  a  wrong 
coupling  of  the  aspirator  tubes. 


278         THE  INCOME  OE  ENERGY 

together).  Place  the  guinea-pig  in  the  jar  and 
weigh.  During  one  hour  draw  air  through  bot- 
tles 1  to  6  by  placing  an  aspirator  bottle  on  its 
box  and  allowing  the  water  to  flow  from  this 
bottle  to  the  one  remaining  on  the  desk.  The 
rubber  connecting  tube  must  be  changed  when 
the  aspirator  bottles  are  changed.  After  one 
hour  weigh  bottle  3,  and  bottles  4  and  5. 
Tabulate  results  as  follows : 


grams 


Weight  of  jar  and  guinea-pig  at  beginning 
"  "  "  end     .     . 


Loss 


Wt.  of  bottle  3  (sulph.  acid)  at  beginning 
"  "  "  end     .     . 

Gain  (=  water  absorbed)      .     .     . 

Weight  of  bottles  4  and  5  at  beginning     . 
"  "  "        end     .     .     . 

Gain  (=  carbon  dioxide  absorbed) 

Total  water  and  carbon  dioxide  absorbed 
Loss  in  weight  of  jar  and  guinea-pig     .     . 
Difference  (=  oxygen  absorbed)     . 
Respiratory  quotient 


Metabolism 

Effect  of  Muscular  Exercise  on  the  Oxygen,  Car- 
bon  Dioxide,  and  Water   of  the    Respired  Air.  — 

Repeat  the  estimation  of  oxygen,  carbon  dioxide, 


RESPIRATION  279 

and  water  in  the  respired  air  (p.  277),  slowly 
turning  the  guinea-pig  jar  from  side  to  side,  so 
that  the  animal  shall  be  kept  in  gentle  motion 
during  an  hour. 

The  excretion  of  carbon  dioxide  is  increased  by 
muscular  exercise. 

Individual  Level  of  Proteid  Metabolism.  —  Each 
group  of  eight  students  will  select  two  subjects 
for  experiment.  They  should  be  thin  men  in 
good  health.  Let  each  subject  collect  the  twenty- 
four  hours'  urine  in  a  thoroughly  clean  bottle  of 
about  2000  c.c.  capacity.  Measure  the  quan- 
tity. Determine  in  a  measured  portion  of  the 
total  mixed  urine  the  quantity  of  urea  (hypobro- 
bromite  method).  Calculate  the  nitrogen  in  the 
urea.  Add  2.5  grams  for  the  nitrogen  excreted 
in  the  faeces,  sweat,  and  as  uric  acid  in  the 
urine. 

Eepeat  these  determinations  for  three  days,  the 
subject  maintaining  his  usual  diet  and  mode  of 
life. 

The  excretion  of  nitrogen  will  probably  be 
found  to  be  fairly  uniform  in  each  individual 
though  the  different  nutritive  habits  of  different 
individuals  may  cause  them  to  be  on  different 
proteid  planes,  characterized  by  high,  medium,  or 
low  nitrogen  excretion. 

Nitrogenous     Equilibrium.  —  When     the     daily 


280  THE   INCOME   OF   ENERGY 

excretion  of  nitrogen  has  been  found  to  be  fairly 
uniform,  place  the  subject  upon  a  simple  diet 
of  eggs,  bread,  milk,  and  butter,  containing  as 
much  nitrogen  as  he  excretes.1 

The  diet  may  be  chosen  from  the  following- 
table.2 

The  relative  proportion  of  proteid,  fat,  and  car- 
bohydrate per  day  should  be  about  as  follows : 

Proteid 100  grams 

Fat 100  grams 

Carbohydrate    .     .     .     250  grams 

450  grams 

Eepeat  the  determination  of  urea  in  the  urine 
during  four  more  days.3     Calculate  the  nitrogen 

1  Owing  to  the  variation  in  the  nitrogen  content  of  meats, 
they  should  be  omitted. 

Physiological  heat  values  :  — 

1  grain  proteid  =  4000  small  calories 

1      "    fat  =  9423      " 

1       "    carbohydrate  zr  4182      "  " 

Proteids  contain  about  16  per  cent  nitrogen.  Hence  to  obtain 
the  amount  of  metabolized  proteid  from  the  nitrogen  in  the 
urine  multiply  the  latter  by  6.25. 

In  one  pound  there  are  453.6  grams. 

2  Coffee  and  tea  contain  so  little  nitrogen  that  they  may  be 
added  to  the  diet  in  small  amounts  to  suit  the  individual  taste. 

3  The  twenty-four  boms  should  begin  in  the  morning  im- 
mediately after  passing  the  mine  excreted  dining  the  night. 


RESPIRATION 


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282  THE   INCOME   OF   ENERGY 

excreted  in  urea,  adding  2.5  grams  for  the  nitro- 
gen of  the  faeces,  sweat,  uric  acid,  etc. 

It  will  probably  be  found  that  the  nitrogen 
excreted  equals  that  ingested  (nitrogenous  equi- 
librium). 

Effect  of  Muscular  Exercise  on  Proteid  Metab- 
olism. —  On  the  third  day  of  the  preceding  ex- 
periment, the  subject  should  take  an  unusual 
amount  of  measurable  exercise.  Hill-climbing 
is  a  suitable  form.  The  protocol  of  the  experi- 
ment must  contain  an  approximate  estimate' of 
the  work  done  in  foot  pounds. 

It  will  be  found  that  muscular  work,  unless 
pushed  to  great  fatigue,  does  not  increase  pro- 
teid metabolism,  as  measured  by  the  nitrogen 
excreted. 


PART   III 

THE   OUTGO   OF   ENERGY 


PART    III 
THE    OUTGO    OF   ENERGY 

I  Animal  Heat 

Regional  Temperature.  —  Record  the  tempera- 
ture taken  with  a  clinical  thermometer  placed 
under  the  tongue,  in  the  axilla,  and  in  the 
rectum. 

Effect  of  Hot  and  Cold  Drinks  on  the  Tempera- 
ture of  the  Mouth.  —  Record  the  temperature 
taken  under  the  tongue  soon  after  drinking  (1) 
cold  water.  (2)  warm  water. 

Hourly  Variation.  —  Record  the  temperature 
taken  under  the  tongue  every  two  hours  through 
the  day  and  plot  the  results  on  clinical  tempera- 
ture paper. 

Reaction  of  Cold  and  Warm  Blooded  Animals  to 
Changes  in  the  External  Temperature.  —  1.  Record 
the  temperature  in  the  gullet  of  a  frog  placed  in 
water  of  varying  temperature.  2.  Record  the 
(rectal)  temperature  of  a  guinea  pig  in  a  bath  at 
40°,  gradually  cooled  to  15°  C. 

Chemical  Action  the  Source  of  Animal  Heat.  — 
Calculate  the  heat  values  observed  by  Rubner  1 

1  Rubnee  :  Zeitschrift  fur  Biologie,  1894,  xxx,  p.  134. 


286  THE   OUTGO   OF   ENERGY 

in  a  dog  weighing  11.8  kg.,  receiving  580  gms. 
flesh  daily.1 


Date 
1890. 

Nitrogen 
excreted. 

Fat 
C 

Calories 
from  Proteid  ;  from  Fat. 

Total 
calories, 

April  11 

18.75 

14.6 

12 

17.39 

18.2 

13 

19.43 

13.7 

14 

18.35 

17.5 

15 

18.57 

17.5 

16 

18.50 

16.8 

17 

18.31 

17.1 

Compare  above  results  with  those  actually  ob- 
tained by  Eubner  when  the  dog  was  placed  in 
the  calorimeter. 


Date 
1890. 

Heat  given 
to  calorimeter. 

Heat  lost  in 
ventilation.        evaporation 
of  water. 

Total 
calories 
in  24  hrs, 

ril  12 

469.4 

44.8 

165.1 

679.4 

13 

483.0 

56.4 

148.6 

687.9 

14 

455.3 

32.9 

178.0 

666.1 

15 

485.1 

34.4 

179.1 

698.7 

16 

447.9 

34.7 

199.3 

681.8 

17 

465.9 

34.1 

174.2 

674.2 

18 

456.9 

35.1 

187.3 

679.4 

1  1  gm.  proteid  =  4.1  cal.  (Rubner  used  4.0      cal.) 
1   "        fat       =  9.3    "    (      "  "     9.423  "  ) 

To  find  the  fat  from  the  carbon  multiply  the  carbon  by  1.3 
(fat  contains  76.5  per  cent  of  carbon). 


THE   ELECTROMOTIVE    PHENOMENA  287 


II 


THE  ELECTROMOTIVE   PHENOMENA   OF 
MUSCLE   AND   NERVE 

The  stored  energy  of  muscle  is  set  free  in  molec- 
ular movement,  —  heat,  chemical  action,  and 
electricity,  —  and  in  mechanical  work,  the  change 
in  form.  It  will  be  convenient  to  consider  the 
electromotive  phenomena  first. 

The  Demarcation  Current  of  Muscle 

Demarcation  Current  of  Muscle.  —  1.  Mount 
two  non-polarizable  electrodes.  Connect  them 
to  the  capillary  electrometer  through  a  short- 
circuiting  key.  Remove  a  sartorius  muscle.  Cut 
off  each  end  with  a  sharp  knife  by  a  clean  cut  at 
right  angles  to  the  fibres.  Observe  that  the 
muscle  is  thereby  converted  into  a  "  muscle 
prism."  It  possesses  two  artificial  cross-sections, 
at  each  of  which  the  muscle  has  been  injured, 
and  is,  in  fact,  dying,  and  an  uninjured  natural 
longitudinal  surface.  Place  the  muscle  across 
the  electrodes  so  that  the  cross-section  rests  on 
one  electrode  and  the  middle  of  the  longitudinal 
surface  rests  on  the  other.  Bring  the  meniscus 
of  the  capillary  into  the  field.  Note  its  position 
on  the  micrometer  scale.     Open  the  key. 


288  THE   OUTGO   OF   ENERGY 

The  meniscus  will  be  displaced  in  the  direc- 
tion indicating  a  higher  potential  at  the  middle 
or  "  equator  "  of  the  longitudinal  surface  than 
at  the  cross-section.  Note  the  divisions  of  the 
scale,  traversed  by  the  meniscus  —  the  displace- 
ment is  proportional  to  the  difference  of  potential. 

2.  Move  the  electrode  on  the  longitudinal  sur- 
face a  few  millimetres  towards  the  cross-section. 
Determine  the  difference  of  potential  here.  It 
will  be  less  than  before.  Measure  the  potential 
in  similar  manner  at  intervals  of  5  mm.  between 
this  point  and  the  cross-section.  On  co-ordinate 
paper  set  down  on  the  abscissa  the  number  of 
millimetres  from  equator  to  cross-section.  Set 
down  as  ordinates  the  number  of  divisions  of  the 
micrometer  scale  traversed  by  the  meniscus  when 
the  electrode  on  the  longitudinal  surface  is  placed 
successively  on  the  equator,  and  at  intervals  of  5 
mm.  between  equator  and  cross-section.  Draw 
the  curve  uniting  the  summits  of  the  ordinates. 

As  the  cross-section  is  approached,  the  curve  of 
potential  will  fall  more  and  more  rapidly.  The 
centre  of  the  cross-section  is  negative  towards 
the  outer  parts  of  the  section.  Points  on  the 
equator,  or  equidistant  from  it,  have  the  same 
potential.  Points  on  the  longitudinal  surface 
at  different  distances  from  the  equator,  and  on 
the  cross-section  at  different  distances  from  the 


THE    ELECTROMOTIVE    PHENOMENA  289 

centre  of  the  section,  show  a  slight  difference  of 
potential. 

Prove  these  several  statements. 

Oblique  Section.  —  When  the  artificial  cross- 
section  is  oblique  to  the  long  axis  of  the  muscle, 
the  maximum  difference  of  potential  is  no  longer 
at  the  equator  and  the  centre  of  the  cross-section. 
The  most  positive  point  is  on  the  longitudinal 
surface  near  the  obtuse  angle  made  by  the  oblique 
section,  and  the  most  negative  point  is  on  the 
cross-section  near  the  acute  angle.  The  structure 
of  certain  muscles,  the  frog's  gastrocnemius,  for 
example,  is  such  as  to  make  their  natural  cross- 
section  oblique.  In  consequence,  their  differ- 
ences of  potential  are  not  distributed  as  in  a 
regular  parallel-fibred  muscle  like  the  sartorius. 
In  the  gastrocnemius,  owing  to  the  peculiar  inser- 
tion of  the  muscle  fibres  into  the  tendon,  the 
upper  end  of  the  muscle  is  really  the  middle  of 
the  longitudinal  section,  while  the  lower  end 
is  the  acute  angle  of  an  oblique  cross-section. 
When  the  ends  are  connected  with  an  electrom- 
eter, a  strong  current  is  observed  flowing  (out- 
side the  muscle)  from  the  upper  to  the  lower  end. 

Uninjured  Muscle.  —  Prepare  .a  sartorius  muscle 
with  extreme  care  to  prevent  injury.  Connect 
the  tendon  (the  natural  "cross-section")  and 
the   longitudinal   surface  with  the  electrometer 

19 


290  THE    OUTGO    OF   ENERGY 

through  a  short-circuiting  key.  Note  the  posi- 
tion of  the  meniscus  on  the  micrometer  scale. 
Open  the  short-circuiting  key. 

The  meniscus  will  move  but  little.  It  will  not 
move  at  all,  provided  the  muscle  has  not  been 
injured;  but  the  difficulty  of  preparation  is  such 
that  some  difference  of  potential  will  probably 
appear. 

Close  the  key.  Injure  the  muscle  by  drawing 
a  hot  wire  across  one  end.     Open  the  key. 

A  strong  demarcation  current  will  appear. 

Stimulation  by  Demarcation  Current.  —  1.  Make 
a  nerve-muscle  preparation  (sciatic  nerve  and 
gastrocnemius  muscle).  Let  the  nerve  near  the 
muscle  touch  a  cross-section  of  the  sartorius. 
Now  let  the  end  of  the  nerve  fall  on  the  longi- 
tudinal surface  near  the  equator. 

The  gastrocnemius  will  contract;  the  nerve 
acts  as  a  conductor  between  the  positive  longi- 
tudinal  surface   and   the   negative    cross-section. 

It  should  be  pointed  out  that  the  conclusion 
here  drawn  is  not  entirely  free  from  criticism. 
The  muscle  is  a  conductor  as  well  as  the  nerve, 
and  may  close  the  demarcation  current  of  the 
nerve,  as  the  nerve  may  close  that  of  the  muscle. 
Thus  it  is  possible  that  the  nerve  is  stimulated 
by  its  own  demarcation  current.  The  former 
explanation   is  the  more  probable. 


THE    ELECTROMOTIVE   PHENOMENA  291 

2.  Place  non-polarizable  electrodes  on  the 
longitudinal  surface  and  cross-section  of  the 
sartorius.  Fasten  the  wires  of  the  stimulating 
electrodes  in  the  binding  posts  of  the  non-polar- 
izable  electrodes.  Drop  the  nerve  of  the  nerve- 
muscle  preparation  across  the  electrode  points. 

The  gastrocnemius  will  contract  when  the 
nerve  bridges  the  space  from  one  electrode  to 
the  other,  and  thus  completes  the  circuit  be- 
tween the  longitudinal  surface  and  cross-section 
of  the  sartorius. 

3.  Place  a  little  0.6  per  cent  solution  of  sodium 
chloride  in  a  porcelain  dish.  Fasten  one  end  of 
the  sartorius  gently  between  two  pieces  of  cork 
in  the  jaws  of  the  muscle  clamp.  Bring  the 
muscle  over  the  saline  solution.  Make  a  fresh 
clean  cross-section,  and  lower  the  clamp  on  its 
stand  until  the  cross-section  dips  (not  too  far) 
into  the  solution. 

The  muscle  will  twitch.  The  twitch  will  pull 
the  end  of  the  muscle  out  of  the  solution.  When 
the  muscle  relaxes,  the  contact  between  positive 
longitudinal  surface  and  negative  cross-section 
is  once  more  made  by  the  saline  solution,  the 
current  of  rest  flows  from  the  point  of  higher  to 
•the  point  of  lower  potential,  and  again  stimulates 
the  muscular  tissue  through  which  it  passes. 
Thus  the  muscle  is  stimulated  by  its  own  cur- 


292  THE    OUTGO    OF    ENERGY 

rent.  A  long  series  of  contractions  may  be 
secured.  Other  liquid  conductors  will  serve. 
When  the  solution  touches  only  the  cross-sec- 
tion, there  is  no  contraction. 

4.  Prepare  a  fresh  sartorius  muscle  with  bony 
attachments.  Fasten  the  pelvic  end  in  the 
muscle  clamp.  Make  a  fresh  cross-section  in 
the  first  sartorius.  Hold  the  tibial  end  of  the 
second  muscle  in  such  a  way  that  the  muscle 
lies  horizontally  with  its  upper  surface  some- 
what concave.  Against  this  surface  bring  the 
fresh  cross-section  of  the  first  sartorius.  The 
longitudinal  surface  will  naturally  also  touch 
to  some  extent. 

The  second  muscle  will  close  the  circuit  be- 
tween longitudinal  surface  and  cross-section  of 
the  first,  and,  if  very  irritable,  both  muscles  will 
contract. 

Interference  between  the  Demarcation  Current 
and  a  Stimulating  Current  ;  Polar  Refusal.  —  Con- 
nect a  dry  cell  through  an  open  key  with  the 
0  and  1  metre  posts  of  the  rheochord  (Fig.  46). 
Mount  two  non-polarizable  electrodes,  and  con- 
nect them  through  a  pole-changer  (with  cross- 
wires)  to  the  positive  post  and  slider  of  the 
rheochord.  Tie  a  thick  cotton  thread  to  the 
foot  of  the  positive  electrode  in  such  a  way 
that  the  thread  shall  hang  down  in  a  small  loop. 


THE   ELECTROMOTIVE   PHENOMENA  293 

Let  a  sartorius  muscle  rest  on  a  clean  glass 
plate.  Make  an  artificial  cross-section  by  draw- 
ing a  hot  wire  across  the  muscle  near  the  pelvic 
end.  Pass  the  loop  of  thread  on  the  positive 
electrode  over  the  muscle  about  5  mm.  from  the 
thermal  cross-section.  Let  the  negative  electrode 
rest  on  the  cross-section.  Arrange  the  rheochord 
for  weak  currents.  Moisten  the  electrodes  with 
normal  saline  solution.     Close  the  key. 

The  usual  closing  contraction 
will  be  absent  (polar  refusal). 

Note  that  the  galvanic  cur- 
rent is  now  passing  through 
the  muscle  in  an  atterminal 
direction,  i.  e,  towards  the  in-  s — <*  ^Q — ^^ 
jured  portion  (admortal),  while  \^^ 
the  demarcation  current  is 
passing  through  the  muscle  in  Fig.  46. 

the  opposite  direction.  The  two  currents  more 
or  less  compensate  each  other.  Hence,  the  ab- 
sence of  the  closing  contraction.  Observe,  also, 
that  opening  the  key  will  break  the  galvanic  cir- 
cuit, but  that  the  circuit  for  the  demarcation 
current  will  still  be  closed  —  through  non-polariz- 
able  electrodes  and  rheochord. 

Open  the  key. 

An  opening  contraction  will  take  place, 
obviously  because  the  muscle  current  is  no 
longer  compensated. 


294  THE    OUTGO   OF   ENERGY 

Keverse  the  pole-changer,  so  that  the  anode 
lies  at  the  cross-section.  Open  and  close  the 
galvanic  current. 

Contraction  will  take  place  at  closure  only. 
The  electrode  at  the  cross-section  again  refuses. 

2.  Compensation  Method.  —  The  electromotive 
force  of  a  current  of  injury  may  be  expressed  in 
fractions  of  a  Daniell  cell,  or  any  other  constant 
element,  by  bringing  into  the  same  circuit  with  the 

current  of  injury,  but  in  an 
opposite  direction,  so  much 
of  the  current  from  the  cell 
as  will  exactly  balance  the 
current  of  injury,  i.  e.  so 
much  as  will  keep  the  menis- 
cus of  the  electrometer  from 
moving  in  either  a  positive 
or  negative  direction  when 
Fie- 47-  connected  with  the  circuit. 

Prepare  a  sartorius  muscle.  Connect  a  Daniell 
cell  with  the  0  and  10  metre  posts  of  the  rheo- 
chord.  Connect  the  capillary  electrometer  to  a 
closed  short-circuiting  key.  From  the  post  joined 
to  the  capillary  lead  to  the  0  post  of  the  rheo- 
chord.  Connect  the  remaining  post  of  the  key 
to  a  non-polarizable  electrode  placed  on  the  cross- 
section  of  the  muscle.  Join  the  slider  of  the 
rheochord   to    another  non-polarizable    electrode 


THE   ELECTROMOTIVE   PHENOMENA  295 

placed  on  the  equator  of  the  muscle  (Fig.  47). 
Bring  the  slider  to  the  zero  post.  Bring  the 
meniscus  into  the  field.  Note  its  position  on  the 
micrometer  scale.  Open  the  short-circuiting  key. 
When  the  meniscus  comes  to  rest,  move  the  slider 
along  the  rheochord  -until  the  meniscus  returns 
to  its  original  position.  Eead  the  number  of 
millimetres  between  the  positive  post  and  the 
slider.  This  number  divided  by  10,000  is  the 
fraction  of  the  electromotive  force  of  the  Daniell 
cell  (1.1  volt)  necessary  to  balance  the  current  of 
injury  of  the  muscle  (from  0.035  to  0.090  volt). 

Demarcation  Current  of  Nerve 

Place  non-polarizable  electrodes  on  the  cross- 
section  and  longitudinal  surface  of  a  long  piece 
of  sciatic  nerve.  Connect  the  electrodes  through 
a  short-circuiting  key  with  the  electrometer. 
Bring  the  meniscus  into  the  field  and  open  the 
short-circuiting  key. 

The  meniscus  will  move  in  a  direction  indicating 
a  current  in  the  nerve  from  cross-section  to  loncn- 

o 

tudinal  surface,  as  in  muscle. 

Measure  the  electromotive  force  of  this  demar- 
cation current. 

The  demarcation  current  is  much  weaker  in 
nerve  than  in  muscle,  being  in  the  former  about 


296  THE   OUTGO   OF   ENERGY 

0.025  volt,  as  against  about  0.060  volt  in 
muscle.  The  demarcation  current  of  muscle  is 
maintained  in  force  for  a  long  time,  whereas  that 
of  nerve  diminishes  rapidly.  The  nerve  current 
is  restored  on  making  a  fresh  cross-section. 

The  demarcation  current  from  the  cut  branches 
of  a  nerve  may  reach  electrodes  placed  on  the 
main  trunk,  and  thus  confuse  the  electrometer 
measurements.  To  this  same  cause  must  be 
ascribed  the  increased  irritability  observed  in  the 
main  trunk  in  the  neighborhood  of  branches ; 
the  irritability  is  raised  by  the  demarcation  cur- 
rent of  the  severed  branch. 

Nerve  may  be  stimulated  by  its  own  Demarca- 
tion Current.  —  On  a  glass  plate  make  a  U  shaped 
wall  of  normal  saline  clay,  each  limb  about  1  cm. 
long  and  3  or  4  mm.  wide.  Carefully  remove  the 
moisture  between  the  clay  walls  with  filter  paper. 
Lay  the  longitudinal  surface  of  the  nerve  of  a  nerve- 
muscle  preparation  on  one  limb  of  the  U,  and  with  a 
glass  rod  let  the  cross-section  fall  on  the  other  limb. 

When  the  circuit  between  the  cross-section  and 
the  longitudinal  surface  is  completed  by  contact 
with  the  clay,  the  demarcation  current  will 
stimulate  the  nerve,  and  the  resulting  nerve  im- 
pulse will  cause  the  muscle  to  contract. 

Other  Examples.  —  The  dropping  of  the  central 
end  of  the  severed  vagus  nerve  into  the  wound 
from  which  it  was  lifted  has  caused  the  slowing 


THE   ELECTROMOTIVE    PHENOMENA  297 

of  respiration,  presumably  by  the  stimulation  of 
the  nerve  through  the  closure  of  its  own  demar- 
cation current  by  the  lymph  or  blood,  though 
the  possible  influence  of  demarcation  currents 
from  the  wounded  tissues  cannot  be  forgotten. 
Definite  results,  such -as  inhibition  of  the  heart, 
have  not  been  observed  to  follow  the  closure  of 
the  current  of  the  peripheral  segment.  To  avoid 
any  chance  stimulation  from  the  closure  of  the  de 
marcation  current,  nerves  are  sometimes  severed 
physiologically  by  freezing,  —  a  process  wdiich 
not  only  does  not  stimulate,  but  which  does  not 
destroy  permanently  the  conductivity  ;  the  latter 
returns  upon  the  restoration  of  the  nerve  to 
normal  temperature. 

The  olfactory  nerve  of  the  pike  shows  a  strong 
demarcation  current,  as  does  the  optic  nerve. 

Hypotheses  regarding  the  Causation  of 
the  Demarcation  Current 

Make  artificial  cross-sections  in  a  sartorius 
muscle,  and  test  the  difference  of  potential  be- 
tween the  longitudinal  surface  and  a  cross-section 
with  the  electrometer.  Divide  the  muscle,  lonoi- 
tudinally,  and  make  fresh  cross-sections  ;  test  the 
difference  of  potential  again. 

However   small    the    muscle    prism    may    be 


293 


THE    OUTGO   OF   ENERGY 


made,  the  longitudinal  surface  will  still  be  posi- 
tive to  the  cross-section. 

Molecular  Hypothesis.  —  The  fact  that  the 
smallest  possible  muscle  prism  is  still  positive 
on  the  longitudinal  surface,  and  negative  on  the 
cross-section,  suggested  to  DuBois-Keymond  that 
muscle  (and  nerve)  are  composed  of  electrical 
particles  or  molecules  something  like  the  mole- 
cules of  a  magnet.  A  magnet  has  two  poles, 
and,  however  it  may  be  divided,  the  pieces  still 


ill 


mmmmmmmmmw 

■■iBinnnainni 

[■■■■■JMMBIBll 


A 


Fig.  48.    Scheme  of  the  myomeres  ill  a  parallel-fibred  muscle  (Rosenthal). 


possess  a  north  and  a  south  pole.  The  magnet  is 
therefore  believed  to  be  composed  of  molecules, 
each  possessing  a  north  and  a  south  pole.  These 
molecules  lie  with  the  north  poles  all  pointing  in 
one  direction,  the  south  poles  in  the  other.  The 
structure  of  muscle  favors,  in  a  measure,  a  simi- 
lar hypothesis ;  for  it  is  known  that  a  striated 
muscle  consists  of  fibrilhe,  each  of  which  is  com- 
posed of  a  row  of  particles  arranged  in  quite 
regular  fashion.    The  electromotive  molecules,  or 


THE   ELECTROMOTIVE    PHENOMENA 


299 


myomeres,  may  be  conceived  to  be  positive  on 
their  longitudinal  surfaces,  and  negative  on  their 
cross-sections  (Fig.  48).  They  are  assumed  to 
have  their  negative  surfaces  turned  towards  the 
ends  of  the  muscle  or  nerve,  and  the  positive 
equatorial  region  turned  towards  the  longitudi- 
nal surface.  A  non-electric  conducting  substance 
surrounds  them.  An  electrode  placed  on  the 
longitudinal  surface  would  touch  only  the  posi- 
tive sides,  while  an  electrode  placed  on  the  cross- 


Fig.  49.    ScLeme  of  myomeres  in  an  oblique  section  (Rosenthal). 


section  would  touch  only  the  negative  poles. 
However  small  the  muscle  prism  was  made,  the 
relation  would  still  be  the  same.  Thus  the  dis- 
tribution of  potentials  would  correspond  with 
that  actually  observed. 

When  the  cross-section  is  oblique,  the  myo- 
meres at  the  cross-section  are  exposed  as  shown 
in  Fig.  49,  and  the  currents  which  pass  from  the 
longitudinal  surface  of  each  myomere  to  its  cross- 
section  are  added  to  the  main  currents  passing 


300  THE   OUTGO   OF   ENERGY 

from  the  longitudinal  surface  to  the  cross-section 
of  the  "whole  muscle.  The  region  of  maximum 
positive  potential  is  thereby  brought  towards  the 
obtuse  angle  of  the  oblique  cross-section,  and  the 
region  of  maximum  negative  potential  is  dis- 
placed towards  the  acute  angle,  as  actually 
observed. 

When  it  was  found  by  Bernstein,  Hermann, 
and  others,  that  uninjured  muscle  showed  no 
difference  of  potential,  DuBois-Beymond  as- 
sumed that  in  the  natural,  uninjured  state  the 
end  of  the  muscle  in  contact  with  the  tendon 
(the  "  natural  cross- section  ")  is  composed  of  a 
layer  of  molecules  which  have  their  positive  in- 
stead of  negative  surface  turned  towards  the 
tendon. 

The  highly  artificial  and  complicated  structure 
which  DuBois  was  compelled  to  erect  on  this 
foundation  in  order  to  explain  all  the  electrical 
phenomena  of  living  tissue,  cannot  be  discussed 
here.  The  chief  argument  against  the  molecular 
theory  of  muscle  and  nerve  currents  is  that  the 
phenomena  can  be  explained  in  a  simpler  way. 

Alteration  Theory.  —  This  hypothesis,  in  the 
making  of  which  Hermann  and  Hering  have 
been  especially  active,  explains  the  electromo- 
tive forces  of  nerve  and  muscle  by  alterations  in 
the    chemical  composition   of  the  tissue  at  the 


THE   ELECTROMOTIVE    PHENOMENA  301 

cross-section.  When  the  cross-section  is  made, 
the  tissue  next  the  section  passes  through  the 
series  of  catabolic  changes  which  constitute 
muscle  death  ;  carbon  dioxide  is  given  off,  lac- 
tic acid  is  developed,  a  soluble  proteid  is  con- 
verted to  a  less  soluble  form,  etc.  The  contact 
of  this  dying  layer  with  the  uninjured  tissue  is 
believed  to  create  a  difference  of  potential.  The 
potential  difference,  therefore,  appears  at  the  de- 
marcation between  dying  and  uninjured  tissue, 
—  hence  the  term  "demarcation  current."  The 
action  current  finds  its  explanation  in  the  chemi- 
cal changes  accompanying  contraction.  It  would 
be  interesting  to  consider  here  the  parallel  be- 
tween the  chemical  transformations  in  contrac- 
tion and  those  which  usher  in  the  death  of  the 
muscle,  but  we  must  be  content  with  mentioning 
the  apparently  close  relationship.  In  its  most 
general  form,  the  alteration  hypothesis  rests  on 
the  fact  that  living  substance  is  everywhere  the 
seat  of  constant  constructive  and  destructive 
changes.  Where  these  are  nearly  in  equilibrium, 
as,  for  example,  in  the  resting  uninjured  muscle, 
the  tissue  is  equipotential ;  where,  on  the  con- 
trary, either  form  of  chemical  change  has  the 
upper  hand,  as  in  the  explosion  which  we  term 
contraction,  and  in  dying  muscle,  it  is  assumed 
that  a  difference  of  potential  is  created. 


302  THE    OUTGO   OF   ENERGY 

For  many  years  the  weight  of  physiological 
opinion  has  been  largely  on  the  side  of  the  alter- 
ation hypothesis  ;  but  it  would  be  unsafe  without 
further  evidence  to  decide  finally  against  the 
molecular  theory. 

Action  Current  of  Muscle 

The  demarcation  current  (current  of  injury, 
current  of  rest)  just  studied  has  been  shown  to 
be  due  to  the  injury  of  the  tissue.  We  have 
now  to  examine  the  electromotive  forces  which 
appear  when  a  nerve  or  muscle  becomes  active. 

1.  Rheoscopic  Frog.  —  Make  two  nerve-muscle 
preparations,  A  and  B.  Let  the  nerve  of  B 
rest  on  muscle  A.  Stimulate  the  nerve  of  A 
with  single  induction  shocks,  and  with  the 
tetanizing  current. 

Muscle  B  will  contract  once  for  each  contrac- 
tion of  A.  The  current  of  action  of  muscle  A 
stimulates   the  nerve  of  B. 

Secondary  contraction  can  take  place  also  from 
muscle  to  muscle,  but  only  under  circumstances 
that  suggest  increased  irritability,  as,  for  example, 
through  partial  drying.  No  secondary  contrac- 
tion has  been  secured  from  voluntary  muscular 
contraction. 

2.  That  the  stimulus  to  the  nerve  of  the  rheo- 
scopic muscle  is  really  an  electrical  current,  is 


THE    ELECTROMOTIVE    PHENOMENA 


303 


shown  by  the  capillary  electrometer.  Place 
muscle  A  in  the  moist  chamber  upon  two  non- 
polarizable  electrodes.  Let  the  tendon  rest  on 
one  electrode  and  the  equator  on  the  other.    Lead 


T37 


Fig.  50.  The  vibrating  interrupter.  A  platinum  wire  on  the  end  of  a  steel 
spring  dips  into  a  mercury  cup.  By  varying  the  length  of  the  spring,  con- 
tacts from  once  a  second  to  more  than  one  hundred  per  second  may  be 
secured. 

from  the  non-polarizable  electrodes  through  a 
closed  short-circuiting  key  to  the  capillary  elec- 
trometer (the  tendon  should  be  connected  with 


304 


THE   OUTGO    OF   ENERGY 


the  capillary).  Lay  the  nerve  on  stimulating 
electrodes.  Connect  the  latter  with  the  secondary 
coil  of  an  inductorium  arranged  for  single  induc- 


Fig.  51.    The  vibrating  interrupter  arranged  to  make  one  contact  per 

second. 


lion  currents.  Place  the  vibrating  interrupter 
(Figs.  HO,  51)  in  the  primary  circuit.  Bring  the 
meniscus  into  the  field.     Open  the  short-circuiting 


THE    ELECTROMOTIVE    PHENOMENA  305 

key.  The  meniscus  will  be  displaced  by  the 
demarcation  current.  When  the  meniscus  has 
come  to  rest,  stimulate  the  nerve  with  single  and 
repeated  induction  currents. 

With  each  stimulus  there  will  be  a  negative  va- 
riation (action  current)  of  the  demarcation  current. 

When  the  number  of  stimuli  per  second  passes 
a  certain  point,  which  differs  with  different  in- 
dividuals, the  hitherto  separate  excursions  of  the 
meniscus  will  be  fused,  and  a  gray  blur  will 
appear  at  the  end  of  the  vibrating  column. 
Movements  of  this  rapidity  may  of  course  be 
studied  by  photographing  them  on  sensitive  paper 
moving  rapidly  enough  to  draw  the  fused  image 
out  into  a  line  in  which  its  component  oscilla- 
tions are  each  distinct,  or  they  may  be  observed 
directly  by  the  stroboscopic  method. 

The  Action  Current  in  Tetanus ;  Stroboscopic 
Method.  —  1.  If  a  piece  of  thin  black  paper  about 
1  cm.  square  is  fastened  vertically  on  the  end  of 
the  electro-magnetic  signal  lever,  and  the  signal 
placed  in  the  primary  circuit  of  the  inductorium 
arranged  for  tetanizing  currents,  the  piece  of 
paper  will  move  each  time  the  primary  current 
is  made  or  broken  by  the  vibrating  hammer  of 
the  inductorium.  The  movement  is  so  rapid 
that  the  paper  seems  stationary  and  a  gray  haze 
appears  on  its  upper  and  lower  border. 

20 


306  THE   OUTGO   OF   ENERGY 

Connect  the  electrometer  with  the  secondary 
coil  of  the  inductorium,  and  bring  the  vibrating 
meniscus  into  the  field. 

Bring  the  stroboscopic  paper  next  the  acid 
reservoir  of  the  electrometer  at  such  a  height 
that  the  ed^e  of  the  meniscus  shall  be  seen 
through  the  gray  blur.  The  meniscus  will  no 
longer  appear  blurred,  but  will  be  as  sharp  as 
if  the  mercury  were  stationary.  This  appearance 
is  produced  only  when  the  stroboscopic  paper 
and  the  object  seen  by  its  aid  have  the  same 
periodicity  of  vibration.  If  the  periodicity  of 
the  vibrations  is  unequal,  interference  results, 
and  from  this  interference  the  rate  of  vibration 
of  the  observed  body  can  be  calculated.  For 
example,  if  the  observed  body  shows  three  vibra- 
tions per  second,  when  observed  through  the 
stroboscope,  its  rate  is  three  more  per  second 
than  that  of  the  stroboscope. 

In  the  present  instance,  the  meniscus  remains 
apparently  at  rest.  The  number  of  action  cur- 
rents is  therefore  identical  with  the  number  of 
stimuli. 

2.  Rheoscopic  Muscle  Tetanus.  —  The  same 
method  may  be  applied  to  the  analysis  of  the 
rheoscopic  tetanus  in  the  rheoscopic  muscle. 

Place  two  nerve-muscle  preparations  in  the 
moist  chamber.     Place  the  tendon  of  muscle  B 


THE    ELECTROMOTIVE    PHENOMENA 


307 


on  one  electrode  and  the  longitudinal  surface  on 
the  other,  and  connect  them  through  a  short- 
circuiting  key  with  the  electrometer.  Lay  the 
nerve  of  B  on  muscle  A.  Place  the  nerve  of  A 
on  electrodes  connected  with  the  secondary  coil 
(the  coil  should  be  well  over  the  primary). 
Bring  the  meniscus  into  the  field,  and  open  the 
short-circuiting  key.  Place  the  stroboscope,  still 
in  the  primary  circuit,  near  the  meniscus.  Tet- 
anize  the  nerve  of  A. 


Fig.  52. 


For  each  stimulus  received  from  nerve  A, 
muscle  A  contracts ;  the  contractions  are  so  fre- 
quent that  they  fuse  into  tetanus.  At  each 
contraction  of  A,  its  current  of  action  stimulates 
the  nerve  of  B,  and  B  also  contracts.  At  each 
contraction  of  B,  the  action  current  displaces 
the  meniscus,  which  falls  therefore  into  very 
rapid  oscillation.  Observe  the  meniscus  through 
the  stroboscope.  It  will  seem  to  be  standing 
still. 


308  THE   OUTGO    OF   ENERGY 

Thus  the  apparent  continuous  contraction  of 
muscle  B  is  in  reality  a  series  of  simple  contrac- 
tions, as  stated,  corresponding  in  number  to 
the  make  and  break  currents  of  the  inductorium. 
For  each  contraction  there  is  one  action  current 
in  each  muscle.1 

When  a  muscle  and  its  nerve  are  removed 
without  injury  to  the  muscle,  electrodes  placed 
on  the  latter  will  show  no  difference  of  potential, 
as  already  stated  (page  289).  Stimulation  of  such 
a  muscle  through  its  nerve  causes  a  current  of 
action  to  start  at  the  point  at  which  the  nerve 
enters  the  muscle  fibres.  The  contraction  wave 
begins  also  at  this  point,  as  may  be  shown  very 
beautifully  by  "  fixing "  the  contraction  in  the 
muscles  of  certain  insects  by  plunging  the  con- 
tracting muscle  into  a  solution  which  arrests  and 
"  sets  "  the  fibre  instantly.  In  such  cases  fibres 
will  be  found  in  which  the  contraction  wave  is 
caught  at  its  beginning  in  the  neighborhood  of 
the  nerve  end-plate. 

The  action  current,  beginning  at  the  entrance 
of  the  nerve  into  the  muscle  fibre,  passes  in  both 
directions  along  the  fibre.  As  may  be  shown 
with  the  differential  rheotome,  or  by  photograph- 
ing the  meniscus  of  the  capillary  electrometer, 

1  The  experiment  also  demonstrates  that  the  meniscus  has  no 
after  vibra Lions,  but  follows  unerringly  the  changes  of  potential. 


THE    ELECTKOMOTIVE    PHENOMENA  309 

the  current  is  diphasic.  In  the  first  phase,  the 
current  is  directed  away  from  the  nerve,  in 
the  second  phase,  towards  it.  In  extirpated 
muscle,  the  second  phase  is  much  weaker  than 
the  first.  In  normal  muscle  in  situ  (human 
muscle),  this  difference  or  decrement  does  not 
appear. 

The  direction  of  the  current  obtained  with 
the  electrometer  from  the  ivhole  muscle  is  de- 
termined by  the  position  of  the  electrodes  with 
reference  to  the  nerve  equator,  namely,  a  trans- 
verse line  drawn  at  the  mean  distance  from  the 
entrance  of  all  the  nerve  fibres.  Points  nearer 
the  equator  are  negative  to  points  further  away. 

Action  Current  of  Human  Muscle.  —  Cover 
the  brass  electrodes  with  cotton  saturated  with 
saline  solution,  and  connect  them  with  an 
inductorium  arranged  for  tetanizing  currents. 
Close  the  short-circuiting  key  of  the  second- 
ary coil.  Tie  about  each  of  the  non-polarizable 
electrodes  a  piece  of  well  washed  candle-wick  a 
foot  long.  Saturate  the  wick  with  sodium 
chloride  solution.  Place  one  of  these  elec- 
trodes around  the  forearm  near  the  elbow,  the 
other  around  the  wrist.  (The  nerve  equator  lies 
about  the  upper  third  of  the  forearm.)  Connect 
the  electrodes  through  a  short-circuiting  key 
with  the  capillary  electrometer.     Place  the  brass 


310  THE   OUTGO   OF  ENERGY 

electrodes  over  the  brachial  plexus  in  the  axilla. 
Bring  the  meniscus  into  the  field.  Open  the 
short-circuiting  key  leading  to  the  electrometer. 
If  the  meniscus  is  displaced  by  a  skin  (secretion) 
current  bring  it  back  by  means  of  the  pressure 
apparatus.  Set  the  inductorium  in  action.  Open 
the  short-circuiting  key  of  the  secondary  coil, 
thus  stimulating  the  nerves. 

The  meniscus  will  be  displaced  by  an  action 
current. 

Action  Current  of  Heart.  —  1.  Expose  the 
heart  of  a  frog  (page  112).  Lay  the  nerve  of  an 
irritable  nerve-muscle  preparation  on  the  beating 
ventricle. 

During  diastole,  the  rheoscopic  muscle  will  be 
quiet ;  at  each  systole,  it  will  contract. 

2.  Tie  a  cotton  thread  one  inch  long  about  the 
foot  of  each  non-polarizable  electrode,  and  let 
the  ends,  wet  with  normal  saline  solution,  rest 
on  the  beating  heart,  one  on  the  base,  the  other 
on  the  apex.  These  electrodes  will  follow  the 
movements  of  the  heart.  Connect  the  elec- 
trodes through  a  short-circuiting  key  to  the 
electrometer. 

During  the  diastole,  the  meniscus  will  remain 
at  rest.  At  each  beat  of  the  ventricle,  the 
meniscus  will  move  ;  first  in  a  direction  indicating 
that  the  base  is  negative  to  the  apex,  and  then 


THE   ELECTROMOTIVE   PHENOMENA  311 

in  the  opposite  direction.  The  action  current 
passes  over  the  heart  from  base  to  apex. 

These  experiments  show  not  only  that  there 
is  an  action  current  at  each  systole  of  the  heart, 
but  are  evidence  also  that  the  resting  heart 
muscle  is  iso- electric-  (i.  e.  of  uniform  potential). 

The  Action  Current  precedes  the  Contraction.  — 
Expose  the  heart.  Fasten  a  very  fine  copper  wire 
to  the  ventricle ;  the  end  of  the  wire  may  be 
thrust  through  the  tip  of  the  ventricle.     Mount 


Pig.  53.     The  Heart  Lever. 


the  heart  lever  (Fig.  53)  on  a  stand  so  that  the 
writing  point  will  write  on  the  smoked  paper  of 
the  kymograph.  Bring  the  free  end  of  the  wire 
to  the  heart  lever,  on  which  it  may  be  fastened 
with  a  drop  of  colophonium  cement.  Make  a 
nerve-muscle  preparation.  Fasten  the  femur  in 
the  upper  side  of  the  muscle  clamp,  at  right 
angles  to  the  long  axis  of  the  clamp.  Bring  the 
latter  near  the  heart  lever,  so  that  the  nerve  may 
rest  on  the  ventricle.  Fasten  the  tendon  Achilles 
to  the  muscle  lever  by  a  thread  which  passes  over 
the  pulley  on  the  axis  of  the  lever  before  being 


312  THE    OUTGO   OF   ENERGY 

secured  to  the  lever.  Thus  the  muscle,  though 
below  the  lever,  will  pull  it  upwards  when  con- 
traction takes  place.  Let  the  two  writing  points 
be  in  the  same  vertical  line.  Start  the  drum  at 
rapid  speed.  Two  curves  will  be  recorded :  one 
by  the  contraction  of  the  ventricle,  the  other  by 
the  rheoscopic  muscle,  stimulated  to  contract  by 
the  action  current.  The  contraction  of  the  rheo- 
scopic muscle  will  slightly  precede  the  contraction 
of  the  ventricle. 

Current  of  Action  of  Human  Heart.  —  Place 
normal  saline  solution  in  two  beakers.  In  each 
let  the  foot  of  a  non-polarizable  electrode  dip. 
Connect  the  electrodes  through  the  usual  short- 
circuiting  key  with  the  electrometer.  Bring  the 
meniscus  into  the  field.  Let  an  assistant  place  a 
finder  of  each  hand  in  the  saline  solution. 

When  the  short-circuiting  key  is  opened  the 
meniscus  will  be  displaced  by  the  skin  (secretion) 
current.  Careful  observation  will  show  also  a 
periodic  variation  synchronous  with  the  systole 
of  the  heart. 

The  diphasic  character  of  the  action  current  of 
the  heart,  shown  so  well  by  the  capillary  elec- 
trometer to  the  unaided  eye,  appears  even  more 
clearly  when  the  movements  of  the  meniscus  are 
recorded  by  projecting  them  on  a  quickly  moving 
photographic  plate.     By  photography,  too,  the  di- 


THE    ELECTKOMOTIVE   PHENOMENA 


o-i  o 


phasic  character  of  the  action  current  in  the  more 
rapidly  contracting  skeletal  muscle  is  made  visible, 
and  the  form  of  the  action  current  wave  recorded. 
Before   the  capillary  electrometer  was   used  for 


Fig.  54.    Scheme  of  differential  rheotome. 

this  purpose,  the  differential  rheotome  of  Bern- 
stein was  employed.  This  celebrated  invention 
consists  of  a  wheel  which  revolves  at  uniform 
speed  and  carries  contacts  by  which  the  primary 
circuit  of  an   inductorium   and    a   galvanometer 


314  THE    OUTGO   OF   ENERGY 

circuit  may  be  made.  By  means  of  the  induc- 
torium,  the  muscle  is  stimulated  at  one  end. 
The  galvanometer  records  the  current  of  action 
by  means  of  electrodes  placed  at  the  other  end 
of  the  muscle.  The  position  of  the  galvanometer 
contact  on  the  wheel  can  be  shifted  nearer  to  or 
farther  from  the  stimulating  contacts ;  thus  the 
interval  between  stimulation  and  the  making  of 
the  galvanometer  circuit  may  be  chosen  at  will, 
and  the  electromotive  force  at  any  point  in  the 
action  wave  registered.  By  repeatedly  changing 
the  interval,  the  several  portions  of  the  wave 
can  be  investigated  successively,  and  the  results 
plotted.  With  Hermann's  rheotachygraph,  the 
whole  electrical  change  may  be  recorded  at  one 
time.  In  this  instrument  the  stimulating  con- 
tacts revolve  rapidly,  and  the  galvanometer  con- 
tact less  rapidly,  so  that  the  interval  between 
stimulation  and  the  closure  of  the  galvanometer 
continually  alters.  The  effect  of  the  electrical 
change  on  the  galvanometer  is  thus  prolonged  so 
that  the  galvanometer  mirror  is  able  to  follow  it. 
The  results  from  these  different  methods  agree 
in  showing  that  the  electrical  change  sweeps 
over  the  muscle  (and  nerve),  in  the  form  of  a 
wave  at  a  rate,  in  frog's  muscle,  of  about  three 
metres  per  second.  The  duration  of  the  wave 
is  from  0.0033  to  0.0040  second.     The  ascent  is 


THE   ELECTROMOTIVE    PHENOMENA  315 

quicker  than  the  descent.  The  latent  period  is 
probably  absent ;  the  process  begins  as  soon  as 
the  stimulus  reaches  the  muscle.  The  electro- 
motive force  of  the  action  current  for  a  single 
contraction  of  the  frog's  gastrocnemius  is  about 
0.08  volt. 

Direct  stimulation  of  the  whole  of  a  normal 
uninjured  muscle  produces  no  action  current 
whatever,  because  the  whole  muscle  becomes 
active  at  the  same  moment. 

Action  Current  of  Xerve 

1.  Negative  Variation.  —  Sever  the  nerve  of  a 
nerve-muscle  preparation  close  to  the  muscle, 
and  lay  the  nerve  in  the  moist  chamber  on  non- 
polarizable  electrodes  placing  the  equator  on  one 
and  a  cross-section  on  the  other.  Lead  them 
through  a  short-circuiting  key  to  the  capillary 
electrometer.  Place  a  second  pair  of  non-polar- 
izable  electrodes  near  the  other  cross-section 
of  the  nerve.  Connect  this  second  pair  to  the 
secondary  coil  of  an  inductorium.  Connect  the 
primary  coil  through  a  key  and  the  wheel  inter- 
rupter with  a  dry  cell.  Bring  the  meniscus  into 
the  field.  Open  the  short-circuiting  key.  The 
meniscus  will  be  displaced  by  the  demarcation 
current.  Stimulate  the  nerve  with  induction 
shocks  at  different  rates. 


316  THE   OUTGO   OF  ENERGY 

A  negative  variation  will  be  observed  each 
time  the  nerve  is  stimulated. 

2.  The  current  of  action  is  not  dependent  on 
the  electrical  stimulation,  but  is  an  expression  of 
the  changes  in  the  nerve  which  constitute  the 
nerve  impulse.  It  follows  mechanical  as  readily 
as  electrical  stimulation. 

Lead  to  the  capillary  electrometer  from  non- 
polarizable  electrodes  placed  on  the  longitudinal 
surface  and  cross-section.  Note  the  position  of 
the  meniscus.  Stimulate  the  nerve  mechanically 
by  snipping  the  end  with  the  scissors. 

There  will  be  a  negative  variation  as  before- 
Positive  Variation.  —  The  direction  of  the  cur- 
rent of  action  is  not  always  opposite  to  that  of 
the  demarcation  current.  Biedermann  obtained 
a  current  in  the  positive  direction  on  stimulating 
the  nerve  to  the  abductor  muscle  in  the  lobster. 
In  the  tortoise,  the  cardiac  auricle  may  be  cut 
away  from  the  sinus,  without  injury  to  the  cor- 
onary nerve,  which  in  this  animal  carries  to  the 
auricle  the  cardiac  fibres  of  the  vagus.  After 
this  operation,  the  auricle  and  ventricle  remain 
motionless  for  a  time.  In  a  heart  thus  prepared, 
Gaskell  made  a  thermal  cross-section  by  im- 
mersing the  tip  of  the  auricle  in  hot  water,  and 
led  the  demarcation  current  to  a  galvanometer. 
The  stimulation  of  the  vagus  in  the  neck  —  the 


THE    ELECTROMOTIVE   PHENOMENA  317 

heart  still  resting  —  caused  a  marked  increase  in 
the  demarcation  current,  in  other  words,  a  posi- 
tive variation.  No  visible  change  in  the  form  of 
the  heart  was  observed. 

Positive  After  Current.  —  Compensate  the  de- 
marcation current  of  nerve  by  the  method  de- 
scribed on  page  294.  When  compensation  is 
secured,  note  the  position  of  the  meniscus  on  the 
scale,  and  tetanize  the  nerve.  The  meniscus  will 
be  displaced  by  the  current  of  action.  Note  the 
direction  of  the  current.  Break  the  stimulating 
current.  The  meniscus  will  return  to  and  pass 
the  position  which  it  held  when  the  demarca- 
tion current  was  compensated,  showing  thus  a 
current  opposed  in  direction  to  the  action 
current. 

The  positive  after  current  is  absent  in  weak- 
ened or  fatigued  nerves. 

Contraction  secured  with  a  Weaker  Stimulus 
than  Negative  Variation.  —  Place  the  non-polariz- 
able  electrodes  on  the  longitudinal  surface  of  the 
nerve  of  a  nerve-muscle  preparation.  Connect 
them  through  the  usual  short-circuiting  key 
with  the  electrometer.  Bring  the  meniscus  into 
the  field.  Arrange  the  inductorium  for  break 
currents.  Place  the  secondary  coil  some  dis- 
tance from  the  primary.  Stimulate  the  nerve 
in   the   extrapolar   region.     Approach    the   coils 


318  THE   OUTGO    OF    ENERGY 

until  the  threshold  value  is  reached  and  the 
muscle  contracts. 

At  the  threshold  value  of  muscular  contrac- 
tion, the  current  of  action  in  the  nerve  will  not 
yet  be  demonstrable.  The  coils  must  be  still 
nearer  together  before  the  action  current  be- 
comes visible. 

This  experiment  has  a  certain  suggestive 
value.  It  would  not,  however,  be  safe  to  con- 
clude from  it  that  the  action  current  is  not 
an  essential  part  in  the  passage  from  the  resting 
to  the  active  stage.  The  failure  to  recognize  the 
action  current  probably  lies  in  the  method. 

Current  of  Action  in  Optic  Nerve.  —  Place  two 
non-polarizable  electrodes  in  the  moist  chamber, 
and  connect  them  through  a  short-circuiting  key 
with  the  capillary  electrometer.  Eemove  the 
eye  of  the  frog,  together  with  a  portion  of  the 
optic  nerve,  and  lay  the  preparation  on  the  elec- 
trodes in  the  moist  chamber,  letting  the  edge  of 
the  cornea  touch  one  electrode  and  the  optic 
nerve  the  other.  Cover  the  electrodes  and  the 
preparation  with  a  black  pasteboard  box  or 
other  opaque  screen  to  shut  off  the  light.  Note 
the  position  of  the  meniscus  in  the  field  of 
the  microscope.  Open  the  short-circuiting  key. 
A  demarcation  current  from  the  injured  optic 
nerve    to    the  cornea    will    be    indicated.      Ee- 


THE    ELECTROMOTIVE    PHENOMENA  319 

move  the  box  so  that  light  shall  fall  on  the 
retina. 

The  demarcation  current  will  undergo  a  nega- 
tive variation. 

Shut  off  the  light  by  replacing  the  box. 

There  will  now  be  a,  positive  variation. 

Currents  of  action  have  also  been  demonstrated 
in  the  central  nervous  system.  Gotch  and 
Horsley  find  that  when  the  spinal  cord  of  the 
monkey  is  severed,  and  non-polarizable  electrodes 
are  applied  to  the  longitudinal  surface  and  the 
cross-section,  a  negative  variation  of  the  current 
of  injury  appears  whenever  the  cortex  of  the 
cerebrum  is  stimulated  in  the  neighborhood  of 
the  fissure  of  Bolando,  — the  "motor  "  region.  A 
considerable  decree  of  localization  in  the  cord  is 
possible.  It  may  be  shown  that  the  negative 
variation  from  the  motor  region  of  the  cortex 
descends  the  cord  chiefly  in  the  crossed  pyramidal 
tract,  —  a  collection  of  white  fibres  in  the  lateral 
column  of  the  cord  near  the  gray  matter.  It  is 
known  from  pathological  evidence  that  the  nerve 
impulse  from  the  motor  cortical  cells  passes 
through  these  fibres,  and  the  demonstration  of 
their  negative  variation  justifies  the  hope  that 
this  method  may  be  useful  in  determining  the 
course  of  other  nerve  fibres  in  the  brain  and 
cord. 


320  THE   OUTGO   OF   ENERGY 

Errors  from  Unipolar  Stimulation.  —  Attention 
already  has  been  called  to  the  danger  of  unipolar 
induction  currents  entering  the  electrometer 
circuit  in  observations  of  the  action  current  with 
the  capillary  electrometer  or  galvanometer  (page 
74). 

Place  a  nerve  in  the  moist  chamber.  Connect 
the  capillary  electrometer  through  a  short-circuit- 
iug  key  with  non-polarizable  electrodes  placed  on 
the  longitudinal  surface  and  cross-section,  about 
5  mm.  apart.  Let  a  wire  connected  with  one 
pole  of  the  secondary  coil  rest  on  the  nerve  about 
2  cm.  from  the  non-polarizable  electrodes.  Open 
the  short-circuiting  key.  When  the  meniscus 
has  come  to  rest,  set  the  inductorium  in  action. 

If  the  meniscus  remains  at  rest,  bring  the 
secondary  coil  nearer  the  primary,  until  unipolar 
effects  appear. 

Secretion  Current 

Secretion    Current  from   Mucous    Membrane.  — 

Remove  the  skin  from  the  lower  jaw  of  a  frog,  the 
skull  of  which  has  been  cut  away.  Be  very  care- 
ful not  to  touch  the  tongue  with  metal  instruments 
or  with  fragments  of  skin.  Make  a  normal  saline 
clay  electrode  about  1  cm.  square  and  3  mm. 
thick  on  the  glass  of  the  cork  clamp   near  the 


THE    ELECTROMOTIVE    PHENOMENA  321 

cork.  Lay  the  denuded  jaw  on  the  glass,  and 
turn  the  tongue  forward  with  a  glass  rod  until 
the  tip  can  he  secured  in  the  clamp.  Avoid  all 
roughness.  The  normally  upper  surface  of  the 
tongue  will  now  rest  on  the  clay.  Bring  one 
non-polarizable  electrode  into  contact  with  the 
clay,  and  let  the  other  touch  the  upper  (normally 
lower)  surface  of  the  tongue.  Connect  the  elec- 
trodes through  an  open  key  with  the  capillary 
electrometer.  Bring  the  meniscus  into  the  field, 
and  note  its  position  on  the  micrometer  scale. 
Close  the  key. 

A  strong  difference  of  potential  will  be  shown. 
The  normal  under  surface  is  usually  positive 
towards  the  normal  upper  surface. 

The  difference  of  potential  thus  demonstrated 
is  probably  chiefly  due  to  secreting  glands  in  the 
mucous  membrane.  If  the  "secretion  current" 
is  compensated  after  the  general  compensation 
method  described  on  page  294,  and  the  glosso- 
pharyngeal nerve  then  stimulated,  the  electrom- 
eter will  show  an  electromotive  force,  in  a 
direction  opposite  to  the  original  difference  of 
potential,  —  in  other  words,  a  "  negative  variation." 

Negative  Variation  of  Secretion  Current. — Place 

a  frog  curarized  until  voluntary  motion  is  just 

paralyzed  back   uppermost    on    the   frog   board. 

Strip    the    skin    from    one    thigh,   and    expose 

21 


322  THE    OUTGO    OF    ENERGY 

the  sciatic  nerve  of  this  side.  Place  non-polar- 
izable  electrodes  on  the  bare  muscle  of  the 
thigh  and  on  the  skin  of  the  leg.  Connect  the 
electrodes  to  a  rheochord  arranged  for  compensa- 
tion by  the  bridge  method,  as  shown  in  Fig.  47. 
Place  the  capillary  electrometer  in  a  short  cir- 
cuit. Bring  the  meniscus  into  the  field,  and 
note  its  position.  Open  the  short-circuiting  key. 
Move  the  slider  along  the  wire  until  the  meniscus 
returns  to  its  original  position.  Now  stimulate 
the  sciatic  nerve  with  the  tetanizing  current. 

A  negative  variation  will  be  seen.  If  the  skin 
current  was  slight,  the  variation  may  be  positive. 

The  greater  part  of  the  skin  current  is  doubt- 
less a  secretion  current,  but  not  all.  Weak  cur- 
rents have  been  obtained  from  skin  devoid  of 
glands,  for  example,  the  eel's  skin.  Hermann 
attributes  this  current  to  the  degeneration  which 
accompanies  the  change  of  the  nucleated  cells  of 
the  corium  to  the  dead  scales  of  the  outer 
epidermis. 

A  strong  secretion  current  may  be  obtained 
from  the  skin  of  the  foot  (cat).  On  stimulation 
of  the  sciatic  nerve,  the  current  is  increased 
(positive  variation). 

In  the  submaxillary  gland,  the  hilus  is  positive 
to  any  point  on  the  external  surface  of  the  gland. 
Stimulation  of  the  chorda  tympani  nerve,  secre- 


THE    ELECTROMOTIVE    PHENOMENA  323 

tory  fibres  from  which  are  supplied  to  the  gland, 
causes  the  surface  to  become  still  more  negative, 
i.  e.  the  secretion  current  is  increased  (positive 
variation).  Stimulation  of  the  sympathetic,  which 
also  sends  fibres  to  the  gland,  causes  the  secretion 
current  to  lessen  (negative  variation). 

Electrotonic  Currents 

It  has  already  been  shown  that  the  irritability 
and  conductivity  of  the  nerve  are  altered  by  the 


Fig.  55. 

galvanic  current.     So  also  are  the  electromotive 
properties. 

Place  one  pair  of  non-polarizable  electrodes 
near  the  middle  of  a  long  piece  of  extirpated 
nerve,  and  one  other  pair  at  each  end,  on  the 
cross-section  and  longitudinal  surface  as  in  Fig. 
55.  Connect  the  middle  pair  through  a  key 
with  two  dry  cells.  Connect  each  of  the  other 
pairs    through  a    short-circuiting    key    with    a 


324  THE   OUTGO    OF   ENERGY 

capillary  electrometer.  Let  one  observer  watch 
each  meniscus,  while  a  third  experimenter 
manages  the  polarizing  current.  Note  the  posi- 
tion of  each  meniscus.  Open  the  short-circuiting 
keys.  In  each  electrometer,  the  meniscus  will  he 
displaced  by  the  demarcation  current.  It  should 
be  noted  that  the  demarcation  currents  are  of 
opposite  direction,  flowing  in  the  nerve  from  the 
cross-section  towards  the  longitudinal  surface. 
Make  the  polarizing  current. 

When  the  polarizing  current  enters  the  nerve, 
there  will  be  a  twitch  in  each  electrometer, 
caused  by  the  negative  variation  of  the  demar- 
cation current;  this  may  be  neglected.  Each 
meniscus  will  be  displaced;  on  the  side  of  the 
anode  of  the  polarizing  current,  the  demarcation 
current  will  be  reinforced,  but  on  the  side  of  the 
cathode  it  will  be  diminished. 

Thus  the  passage  of  the  galvanic  current 
through  a  part  of  the  nerve  has  polarized  the 
nerve  on  both  sides  of  that  part.  The  extra- 
polar  region  on  the  side  of  the  anode  becomes 
positive ;  the  extrapolar  region  on  the  side  of  the 
cathode  becomes  negative  ;  similar  changes  prob- 
ably occur  in  the  intrapolar  region.  In  short,  an 
electrotonic  current  is  set  up,  having  the  same 
direction  as  the  polarizing  current.  This  electro- 
tonic  current  augments  the  demarcation  current 


THE   ELECTROMOTIVE    PHENOMENA  325 

on  the  side  of  the  anode,  but  is  opposed  to  that 
on  the  side  of  the  cathode.  It  appears  when 
any  two  points  on  the  longitudinal  surface  are 
"  led  off "  to  the  electrometer,  and  is  entirely 
independent  of  the  demarcation   current. 

The  intensity  of  the  electrotonic  current  de- 
pends on  the  intensity  of  the  polarizing  current. 
The  greater  the  separation  of  the  polarizing  elec- 
trodes, the  less  the  electrotonic  effect,  as  might  be 
expected  from  the  great  resistance  of  nerve.  If 
this  factor  be  excluded  by  placing  in  the  circuit 
a  much  greater  resistance  than  that  of  nerve,  the 
electrotonic  effect  will  be  found  to  increase  with 
the  length  of  the  intrapolar  region.  The  electro- 
tonic current  is  absent  in  dead  nerves,  in  strongly 
cooled  nerves,  and  in  those  ligated  between  the 
polarizing  electrodes  and  the  electrodes  leading 
to  the  electrometer. 

In  muscle,  the  electrotonic  currents  are  much 
stronger  than  in  nerve. 

Negative  Variation  of  Electrotonic  Currents  ; 
Positive  Variation  (Polarization  Increment)  of  Polar- 
izing Current.  —  Place  the  polarization  electrodes 
near  one  end  of  the  nerve.  Connect  them  through 
a  short-circuiting  key  with  a  dry  cell.  From  the 
short-circuiting  key  lead  to  a  capillary  electrom- 
eter (Fig.  o6~).  From  the  middle  of  the  nerve 
lead  off  the  electrotonic  current  through  a  short- 


326  THE   OUTGO   OF   ENERGY 

circuiting  key  to  a  second  capillary  electrometer. 
Near  the  other  end  of  the  nerve  place  stimu- 
lating electrodes  connected  with  the  secondary 
coil  of  an  inductorium  arranged  for  tetanization. 
Make  the  polarizing  current.  Open  the  short- 
circuiting  key  leading  to  the  electrotonic  elec- 
trometer, and  note  the  position  taken  by  the 
meniscus  under  the  influence  of  the  electrotonic 
current.      Make  the  tetanizing  current. 


^- z#=J  Q; 


Fig.  56. 

The  strength  of  the  electrotonic  current  will 
be  diminished.  At  the  same  time  the  strength 
of  the  polarizing  current  will  be  increased  (polar- 
ization increment). 

These  are  in  reality  action  currents. 

The  electrotonic  currents  are  absent  in  nerves 
which  lack  a  myelin  sheath.  This  suggests  that 
the  myelin  in  some  way  divides  the  nerve  into  a 
core  and  a  sheath.  If  a  zinc  wire  connecting 
two  electrodes  is  surrounded  by  a  layer  or  sheath 


THE   ELECTROMOTIVE    PHENOMENA  327 

of  saturated  solution  of  sulphate  of  zinc,  there 
will  be  no  polarization,  and  the  current  will  not 
spread  to  any  extent  beyond  the  electrodes.  If, 
however,  the  wire  is  platinum  instead  of  zinc, 
polarization  will  take  place  where  the  current 
passes  from  the  electrodes  through  the  electrolyte 
into  and  out  of  the  wire,  and  the  polarization 
may  be  recognized  by  connecting  the  extrapolar 
region  with  the  electrometer  as  in  the  foregoing 
experiment.  The  resistance  to  the  spread  of  the 
electrotonic  current  in  a  longitudinal  direction  is 
relatively  slight,  so  that  it  passes  almost  instantly 
along  the  core. 

In  nerve,  also,  the  greater  resistance  in  the 
transverse  direction  (five-fold  greater  than  the 
resistance  in  the  longitudinal  direction)  would 
favor  the  spread  of  electrotonic  currents  length- 
wise along  the  nerve. 

Certain  observations  of  Biedermann  make  it 
difficult  to  accept  without  reservation  the  simple 
physical  explanation  just  offered.  For  example, 
the  narcotization  of  a  nerve  with  ether  or  chloro- 
form causes  the  electrotonus  to  disappear  a 
short  distance  from  the  electrodes,  although 
still  strongly  present  in  their  immediate  neigh- 
borhood. These  experiments  cannot  be  discussed 
here,  but  they  indicate  that  to  the  purely  physi- 
cal must  be  added  a  physiological  electrotonus. 


328  THE   OUTGO   OF   ENERGY 

The   Electrotonic   Current   as  a  Stimulus.  —  As 

would  naturally  be  expected,  the  electrotonic 
current  may  be  an  effective  stimulus.  Bring  the 
end  of  an  extirpated  nerve  A  into  contact  with 
the  distal  portion  of  the  nerve  of  a  nerve-muscle 
preparation,  B,  as  in  Fig.  57,  and  place  on  the 
other  end  of  A  non-polarizable  electrodes  joined 
through  a  key  to  a  battery  of  two  cells.  Make 
the  galvanic  current. 
Muscle  B  will  contract. 

The  galvanic  current  polarizes  nerve  A,  and 
the  electrotonic  current  thereby 
set  up  passes  into  the  nerve  of 
B  through  the  contact,  and  occa- 
sions in  nerve  B  an  impulse 
which    descends   to    the   muscle 

Fig.  57. 

and  stimulates  it  to  contract. 

Paradoxical  Contraction.  —  Expose  the  bifur- 
cation of  the  sciatic  nerve  into  tibial  and  peroneal 
branches.  Polarize  either  of  these  branches. 
(The  electrodes  should  not  be  placed  too  near 
the  bifurcation.) 

On  making  and  breaking  the  polarizing  cur- 
rent, the  muscles  supplied  by  each  branch  will 
contract. 

In  this  instance,  the  extrapolar  region  of  the 
branch  polarized  lies  in  part  in  the  main  trunk. 
The  electrotonic  current  there  spreads  into  the 


THE    ELECTROMOTIVE    PHENOMENA  329 

contiguous    axis    cylinders,   anions    them    those 
of  the  other  branch. 


Electeic  Fish 

There  are  several  species  of  fish  which  possess 
the  power  of  discharging  electrical  currents  when 
stimulated.  The  best  known  are  Torpedo,  a  ray 
.found  on  the  coasts  of  Europe  ;  Gymnotus,  the 
electrical  eel  of  South  America ;  and  Malaptera- 
rus  electricus,  a  catfish  found  in  the  Xile  and 
other  African  rivers.  The  electromotive  force  of 
these  fishes  is  derived  from  a  special  organ  placed 
beneath  the  skin.  This  electrical  organ  is  bilat- 
eral  and  is  formed  of  parallel  plates.  One  side 
of  each  plate  receives  a  branch  of  the  electrical 
nerve,  which  in  Malapterurus  is  a  single  great 
axis  cylinder  derived  from  a  giant  nerve  cell. 
The  side  of  the  plate  receiving  the  nerve  becomes 
negative  to  the  other  side  when  the  electrical 
organ  is  active  ;  it  behaves  like  the  negative  plate 
of  the  ordinary  cell.  When  the  nerve  is  at  rest, 
there  is  no  difference  of  potential  in  the  electrical 
organ.  The  discharge  in  the  active  state  is  peri- 
odic, and  may  rise  to  200  per  second.  The  elec- 
tromotive force  is  considerable  :  in  Torpedo,  30-35 
volts,  5  volts  for  each  cubic  centimetre  of  the 
organ,  0.08  volt  for  each  plate.     The  fish  itself 


330  THE    OUTGO    OF   ENERGY 

is  not  injured  by  the  current ;  its  tissues  are 
not  easily  excitable  by  electricity,  though  they 
respond  readily  to  mechanical  stimulation. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Sharp  knife.  Two  dry  cells.  Four  non-polarizable  elec- 
trodes. Simple  key.  Capillary  electrometer.  Co-ordi- 
nate paper.  Millimetre  scale.  Inductorium.  Electrodes. 
Thirteen  wires.  Porcelain  dish.  Muscle  clamp.  Muscle 
lever.  Stand.  Cork.  Kheochord.  Normal  saline  clay. 
Filter  paper.  Wheel  interrupter.  Candle-wick.  Electro- 
magnetic signal.  Pole-changer.  Bent  hooks.  Black  paper 
(stroboscope).  Moist  chamber.  Large  and  small  brass 
electrodes.  Cotton.  Common  salt.  Two  beakers.  Satu- 
rated solution  of  zinc  sulphate.  Cotton  thread.  Frog 
board.  Heart-holder.  Black  box  for  covering  retina. 
Bunsen  burner.     Glass  slide.     Cork  clamp.     Frogs. 


THE    CHANGE   IN   FORM  331 


III 

THE   CHANGE   IN   FORM 

The  change  in  form  or  the  contraction  of  muscle 
is  the  most  conspicuous  of  the  several  ways  in 
which  its  energy  is  set  free.  It  has  already  been 
shown  that  this  change  consists  of  a  shortening 
of  the  contractile  mass  followed  by  a  return  to 
the  original  length.  It  is  necessary  now  to  de- 
termine whether  the  muscle  becomes  smaller  on 
entering  the  active  state  or  whether  the  altera- 
tion in  form  is  simply  a  shifting  —  a  transloca- 
tion —  of  the  muscular  units. 

Volume  of  Contracting  Muscle 

Strip  the  skin  from  the  hind  limb  of  a  frog. 
Hang  the  limb  from  the  hooked  electrode  in  the 
stopper  of  the  volume  tube  (Fig.  58)  and  place 
the  stopper  loosely  in  the  tube.  Hook  the  elec- 
trode at  the  other  end  of  the  tube  into  the  limb 
near  the  foot.  Fill  the  tube  absolutely  full  of 
boiled  normal  saline  solution,  slightly  withdraw- 
ing the  stopper  for  the  purpose.  Eeplace  the 
stopper  in  the  tube  in  such   a   way  that  all  air 


332 


THE    OUTGO    OF   ENERGY 


Fig.  58.     The 
volume  tube. 


bubbles  shall  be  excluded.  If  the  height  of  the 
water-column  in  the  capillary  tube 
does  not  permit  the  meniscus  to  be 
readily  observed,  move  the  glass  rod 
in  the  stopper  in  or  out  until  the 
meniscus  is  adjusted.  Connect  the 
electrodes  with  the  secondary  coil 
of  an  inductorium  arranged  for 
single  induction  currents.  Note 
carefully  the  level  of  the  water  in 
the  capillary  tube.  Stimulate  the 
muscle  with  a  maximal  break 
current. 

The  level  of  the  water  in  the 
capillary  will  not  change.  The 
change  in  the  form  of  the  contracting  muscle 
is  not  accompanied  by  a  change  in  volume.1 


The  Single  Contraction  or  Twitch 

The  change  in  the  form  of  the  muscle  on 
entering  the  active  state  is  usually  studied  from 
the  graphic  record  made  on  a  smoked  surface 
by  a  writing  lever  the  shorter  arm  of  which  is 
attached  to  the  end  of  the  muscle.  Such  a 
record,  it  should  be  remarked,  gives  the  extent 

1  This  experiment  must  not  be  regarded  as  excluding  a  very 
slight  change  in  volume,  because  of  the  difficulty  of  expelling, 
by  boiling  or  otherwise,  all  the  air  in  the  saline  solution. 


THE    CHANGE    IN    FOEM  333 

and  the  time  relations  of  the  shortening,  but  not 
the  thickening  of  the  muscle.     (See  page  339. J 

The  Muscle  Curve.  Prepare  a  gastrocnemius 
muscle  together  with  the  distal  third  of  the 
femur.  Fasten  the  latter  in  the  muscle  clamp. 
Attach  the  tendo  Achillis  to  the  hook  on  the 
muscle  lever  by  means  of  a  fine  copper  wire 
which  should  be  wrapped  round  the  hook  and 
the  end  then  carried  to  the  binding  post  on  the 
muscle  lever.  Place  a  ten-^ram  weight  in  the 
scale-pan.  Connect  the  posts  on  the  clamp  and 
the  lever  with  the  secondary  coil  of  an  inducto- 
rium  arranged  for  maximal  induction  currents. 
In  the  primary  circuit  place  an  electromagnetic 
signal.  Bring  the  writing  points  of  the  signal 
and  the  muscle  lever  against  the  smoked  paper 
in  the  same  vertical  line.  Start  the  drum  at  its 
most  rapid  speed.  Stimulate  the  muscle  with  a 
maximal  break  current. 

The  muscle  will  shorten  and  then  extend, 
marking  a  period  of  rising  energy  and  a  period 
of  sinking  energy.  Note  that  the  period  of  rising 
energy  is  shorter  than  the  period  of  sinking 
energy.  Close  observation  will  show  that  the 
lever  does  not  begin  to  move  at  the  instant  the 
muscle  is  stimulated,  —  there  is  here  an  interval 
or  latent  period. 

The  Duration  of  the  Several  Periods.  —  Turn  to 


334  THE   OUTGO    OF    ENERGY 

the  right  the  screw  at  the  top  of  the  sleeve  bear- 
ing the  recording  drum  until  the  sleeve  is  raised 
from  the  friction  bearing.  The  drum  can  now 
be  "spun."  Start  the  tuning  fork  vibrating, 
spin  the  drum,  lay  the  writing  point  of  the  tun- 
ing fork  on  the  smoked  paper  near  the  line 
traced  by  the  electro-magnetic  signal,  and  stim- 
ulate the  muscle  with  a  maximal  induction 
current. 

An  interval  will  be  found  between  the  moment 
of  stimulation  (marked  by  the  electromagnetic 
signal)  and  the  beginning  of  contraction.  This 
interval  is  the  mechanical  latent  period.  Meas- 
ure its  duration  by  means  of  the  tuning  fork 
curve.  Measure  also  the  duration  of  the  period 
of  rising  energy  and  the  period  of  sinking  energy. 

Helmholtz,  who  first  measured  the  latent  period 
of  frog's  muscle,  found  a  mean  duration  of  0.01 
sec,  while  the  phase  of  rising  energy  measured 
0.04  sec,  and  the  phase  of  sinking  energy  0.05 
sec.  More  recent  measurements  by  Tigerstedt 
and  others  have  reduced  the  latent  period 
given  by  Helmholtz  to  from  0.0025  to  0.005 
sec.  The  interval  observed  grows  less  as  the 
intensity  of  stimulation  is  increased  from  the 
threshold  to  the  maximal  value ;  further  in- 
crease in  intensity  (supermaximal  stimulation) 
causes  no  further  diminution  in  the  latent  period. 


THE    CHANGE    IN    FORM  335 

The  period  is  shorter  at  high  temperatures  than 
at  low,  with  maximal  break  induction  currents 
than  with  make  induction  currents,  with  break 
induction  currents  than  with  closure  of  the  gal- 
vanic current.  Changing  the  load  of  the  muscle 
is   without  effect  on  the   latent  period. 

When  the  muscle  is  stimulated  through  its 
nerve  the  latent  period  is  longer  by  about  0.002 
sec.  than  when  the  electrodes  are  placed  on  the 
muscle  itself  (Bernstein),  due  allowance  being 
made  for  the  time  occupied  by  the  passage  of 
the  nerve  impulse  along  the  trunk  of  the  nerve 
from  the  point  of  stimulation  to  the  muscle.  The 
additional  time  is  taken  perhaps  in  the  passage 
of  the  impulse  through  the  end  plate  into  the 
contractile  substance. 

Griitzner  has  shown  that  the  striated  muscle 
fibres,  particularly  of  vertebrates,  differ  in  their 
histological  elements.  Some  are  rich  in  sarco- 
plasm,  and  when  seen  by  transmitted  light  appear 
cloudy  and  granular ;  others  have  less  sarcoplasm 
and  are  relatively  translucent.  This  difference 
in  structure  is  associated  with  a  striking  differ- 
ence in  the  character  of  the  contraction.  The 
muscles  composed  chiefly  of  turbid  fibres  contract 
slowly,  while  "  clear "  muscles  contract  rapidly 
(compare  page  178).  Thus  in  the  rabbit  the 
duration  of  the    contraction    of   the    red   soleus 


336  THE   OUTGO    OF    ENEKGY 

muscle,  which  is  rich  in  sarcoplasm,  is  about 
1.0  sec,  while  in  the  white  gastrocnemius — a 
"  clear"  muscle  —it  is  0.25  sec.  In  the  frog,  the 
contraction  period  of  the  hyoglossus  is  0.205, 
the  gastrocnemius  0.120,  and  the  gracilis  0.108 
sec.  (Cash).  The  latent  period  is  longer  in  the 
red  muscles.  The  amplitude  of  contraction  is 
less  in  the  red  than  in  the  white. 

The  mixture  of  quickly  and  slowly  contracting 
fibres  in  the  same  muscle  is  sometimes  obviously 
an  advantage.  Thus  in  certain  bivalves  the  quick 
fibres  in  the  shell-closing  muscle  close  the  shell 
rapidly,  and  the  slow  fibres  keep  it  closed  after 
the  contraction  of  the  quick  fibres  has  ceased. 

The  form  of  the  contraction  is  influenced  by 
the  mixture  of  fibres.  The  clear  fibres  reach 
their  maximum  shortening  sooner  than  those 
rich  in  sarcoplasm.  In  some  instances,  indeed, 
the  contraction  curve  may  show  two  summits. 
These  differences  may  perhaps  explain  the  char- 
acteristic differences  in  the  form  of  the  contrac- 
tion wave  of  different  muscles,  observed  by  Cash 
and  others.  The  white  fibres  are  more  easily 
fatigued  than  the  red.  Thus  the  triceps  humeri 
of  the  rabbit  contracts  at  the  beginning  of  stimu- 
lation like  an  unmixed  white  muscle  (quickly), 
hut  later  like  a  red  muscle  (slowly). 

The    Excitation    Wave.  —  Prepare   a    plate    of 


THE    CHANGE    IX    FORM  337 

cork  one  inch  long  and  just  narrow  enough  to  be 
held  in  the  Gaskell  clamp  (Fig.  26).  Smoke  a 
drum.  Raise  the  drum  off  the  friction  bearing 
by  turning  to  the  right  the  milled  screw  at  the 
top  of  the  shaft.  Fasten  the  end  of  a  curarized 
sartorius  muscle  to  the  cork  plate  by  means  of 
two  needles  to  the  ends  of  which  conducting 
wires  are  soldered.  Place  the  preparation  in  the 
Gaskell  clamp  in  such  a  way  that  the  clamp 
shall  compress  the  equator  of  the  muscle  suffi- 
ciently to  prevent  the  passage  of  a  contraction 
wave  from  one  part  of  the  muscle  to  the  other, 
but  not  sufficiently  to  prevent  the  passage  of  the 
excitation.  Let  a  second  pair  of  needle  elec- 
trodes rest  on  the  muscle  near  the  upper  side  of 
the  clamp.  Fasten  the  clamp  to  the  iron  stand. 
Connect  the  two  pairs  of  electrodes  to  the  end 
cups  of  a  pole-changer  (without  cross-wires),  the 
side  cups  of  which  are  connected  with  the  secon- 
dary coil  of  an  inductorium  arranged  for  single 
maximal  induction  currents.  In  the  primary 
circuit  of  the  inductorium  place  the  electro- 
magnetic signal.  Fasten  the  tibial  end  of  the 
muscle    to   a   muscle    lever.     Bring    the   writing 

o  o 

point  against  the  smoked  surface  exactly  under- 
neath the  point  of  the  electro-magnetjc  signal. 
"  Spin "  the  drum  slowly.  Place  the  writing 
point    of   a   vibrating    tuning   fork    against   the 

22 


338  THE    OUTGO    OF    ENERGY 

smoked  paper  below  the  recording  levers.  Stim- 
ulate the  muscle  with  a  maximal  break  current 
first  through  one  pair  of  electrodes  and  then 
through  the  other.  In  each  of  the  resulting 
curves  measure  the  interval  between  stimulation 
and  contraction  (for  method  see  page  184). 

This  interval  will  be  longer  when  the  muscle 
is  stimulated  farther  from  the  portion  the  con- 
traction of  which  is  recorded.  The  difference  is 
the  time  taken  by  the  excitation  to  traverse  the 
part  of  the  muscle  lying  between  the  two  pairs 
of  electrodes.  Measure  the  distance  and  calcu- 
late the  speed  of  the  excitation. 

The  nature  of  the  excitation  process  is  un- 
known. The  current  of  action  has  been  shown 
to  precede  the  visible  change  in  form  of  muscle. 
It  is  usually  assumed  to  be  a  manifestation  of  the 
excitation  process,  but  the  precise  relation  be- 
tween the  two  has  never  been  ascertained.  The 
speed  of  the  excitation  is  the  same  as  that  of  the 
contraction  wave. 

The  Contraction  Wave.  —  Eemove  from  a  CU- 
rarized  frog  the  long  parallel-fibred  muscles  ex- 
tending along  the  inner  side  of  the  thigh  from 
the  pelvis  to  the  tibia.  Let  the  preparation  rest 
horizontally  on  a  glass  plate  supported  on  a  stand. 
With  fine  wire  fasten  near  the  axle  of  each  of 
two  heart  levers  a  small  piece  of  cork  into  which 


THE    CHANGE    IN   FORM  339 

the  point  of  a  long  pin  has  been  thrust.  Place 
the  levers  so  that  the  head  of  the  first  pin  rests 
on  the  muscle  near  one  end,  while  the  head  of 
the  second  pin  rests  near  the  other  end.  Place 
needle  electrodes  at  one  end  of  the  muscle. 
Bring  the  writing  points  of  the  two  levers 
against  a  smoked  drum  in  the  same  vertical  line. 
Let  a  tuning  fork  write  its  curve  near  that  of  the 
muscle  levers.  Set  the  tuning  fork  vibrating. 
Let  the  drum  revolve  rapidly.  Stimulate  the 
muscle  at  one  end  with  a  maximal  make  induc- 
tion current. 

The  lever  near  the  point  of  stimulation  will 
begin  to  rise  before  that  farther  away.  Evidently 
the  contraction  starts  at  the  point  stimulated  and 
spreads  along  the  muscle  in  the  form  of  a  wave 
(compare  pages  308  et  seq.}. 

Determine  the  speed  per  second  of  the  wave 
of  contraction  by  measuring  with  the  tuning-fork 
curve  the  time  occupied  by  the  wave  in  passing 
along  the  muscle  from  one  lever  to  the  other. 

It  is  evident  that  a  lever  resting  on  a  horizontal 
muscle  will  register  the  change  in  form  of  the 
cross-section  on  which  the  lever  lies,  while  a  lever 
attached  to  the  end  of  a  muscle  suspended  verti- 
cally will  be  moved  by  the  change  in  form  of  all 
the  cross -sections  of  which  the  muscle  is  com- 
posed.   The  curves  secured  by  the  two  procedures 


340  THE    OUTGO    OF   ENERGY 

are  similar  in  form,  but  different  in  duration. 
The  curve  of  thickening  is  shorter  by  the  differ- 
ence between  the  time  taken  by  the  contraction 
wave  to  pass  over  the  single  cross-section,  on  the 
one  hand,  and  the  whole  length  of  the  muscle  on 
the  other. 

An  extirpated  muscle  is  apt  to  remain  short- 
ened after  contraction.  To  bring  muscles  back 
to  their  original  length  it  is  usually  necessary  to 
weight  them,  or  —  as  in  the  bodv — to  submit 
them  to  the  pull  of  antagonists.  Even  the 
weighted  muscles  may  return  very  slowly  and 
imperfectly  to  their  normal  length.  This  con- 
tracture, as  it  is  termed,  is  seen  especially  in 
strong  direct  stimulation,  in  poisoning  with  vera- 
trine,  and  as  death  comes  on.  Contracture  is 
not  the  result  of  fatigue,  for  when  the  muscle 
is  repeatedly  stimulated  contracture  diminishes, 
instead  of  increasing.  During  contracture,  the 
irritability  of  the  muscle  for  stimulation  through 
the  nerve  is  diminished. 

Relation  of  Strength  of  Stimulus  to  Form  of 
Contraction  Wave.  —  Fasten  the  femur  of  a  gas- 
trocnemius preparation  in  the  muscle  clamp  and 
attach  the  Achilles  tendon  to  the  muscle  lever 
with  a  fine  copper  wire  the  end  of  which  should 
be  carried  to  the  binding  post  on  the  handle  of 
the  lever.     Connect  this  post  and  that  on  the 


THE    CHANGE    IN    FORM  341 

muscle  clamp  with  the  secondary  coil  of  the  in- 
ductorium.  Bring  the  writing  point  against  the 
smoked  drum.  Stimulate  the  muscle  with  break 
induction  currents  of  varying  intensity  and  record 
the  contraction  curves. 

It  will  be  found  that  the  contraction  is  longer 
with  weak  stimuli  than  with  strong. 

Influence  of  Load  on  Height  of  Contraction.  — 
Attach  a  curarized  gastrocnemius  preparation 
to  the  muscle  lever  and  bring  the  writing  point 
against  a  smoked  drum.  Connect  the  binding 
posts  on  the  lever  and  the  muscle  clamp  with 
the  secondary  coil  of  the  inductorium.  Load 
the  muscle  with  the  lever  and  scale-pan  only. 
With  the  drum  at  rest  record  the  contraction 
on  stimulation  with  a  maximal  induction  current. 
Turn  the  drum  by  hand  one  millimetre.  Place 
a  one-gram  weight  in  the  scale-pan,  and  record 
the  contraction  produced  by  a  make  induction 
current  of  the  same  intensity  as  before.  Con- 
tinue to  add  gram  weights  and  to  record  the 
contractions  until  ten  one-gram  weights  have 
been  placed  in  the  scale-pan.  Now  increase  the 
load  each  time  by  ten  grams,  recording  the  con- 
traction after  each  increase,  until  the  muscle  is 
weighted  with  one  hundred  grams.  (Care  should 
be  taken  not  to  fatigue  the  muscle  by  stimulating 
it  oftener  than  is  necessary  to  obtain  the  record.) 


342  THE    OUTGO    OF   ENERGY 

Within  certain  narrow  limits  the  height  of  the 
contraction  will  be  increased  by  the  increase  in 
the  load.  With  increasing  loads  the  height  of 
contraction  diminishes  at  first  quickly,  and  then 
more  slowly. 

Influence  of  Temperature  on  the  Form  of  the 
Contraction.  —  Prepare  a  gastrocnemius  muscle 
together  with  its  attachment  to  the  femur. 
Fasten  the  femur  in  the  "  muscle  warmer  "  (Fig. 
59).  Tie  the  end  of  a  fine  copper  wire  about 
ten  centimetres  long  around  the  Achilles  tendon. 
Bring  the  wire  through  the  opening  in  the  muscle 
warmer  and  fasten  the  wire  around  the  pulley 
of  the  muscle  lever.  If  the  pulley  is  of  metal 
the  muscle  lever  should  be  supported  on  a  stand 
separate  from  that  bearing  the  muscle  warmer 
or  should  be  otherwise  insulated.  Connect  the 
muscle  warmer  and  the  muscle  lever  with  the 
secondary  coil  of  an  inductorium  arranged  for 
single  induction  currents.  Fill  a  beaker  with 
cracked  i'ce  and  add  a  little  salt.  Immerse  the 
muscle  warmer  in  the  beaker  and  support  the 
latter  on  a  suitable  stand.  Bring  the  writing 
point  of  the  muscle  lever  against  a  smoked 
drum.  Let  the  drum  revolve  at  fairly  rapid 
speed.  Stimulate  the  cooling  muscle  at  inter- 
vals of  5°  with  a  maximal  break  current. 


THE   CHANGE   IN   FORM 


343 


It 


iii 


^^ 


The  Muscle  Warmer. 1  —  A  disk,  supported  by  a 
rod,  bears  three  pins  (Fig.  59).  One  of  the  three  pins 
is  prolonged  and  bent  at  a  right  angle  near  its  lower 
end.  To  the  bend  is  fas- 
tened one  end  of  the  mus- 
cle under  experimentation. 
About  the  other  end  is  tied 
a  fine  copper  wire  which 
passes  through  a  hole  in 
the  disk  to  reach  a  muscle 
lever.  A  second  opening  in 
the  disk  is  provided  with  a 
short  metal  tube,  in  which 
a  thermometer  is  held  by 
a  piece  of  rubber.  The 
bulb  of  the  thermometer 
may  be  placed  on  a  level 
with  the  belly  of  the 
muscle.  When  these  ad- 
justments   are  complete,  a 

glass     cylinder     is     brought  FlG-  59'     The  muscle  warmer; 

J  an  apparatus  for  studying  the  in- 

against     the    Under     Surface  fluence  of  temperature  on  mus- 

„,,        ,.,         ,           ■■•iii  cular  contraction. 

of  the  disk,  where  it  is  held 

in  position  by  the  "spring"  of  the  three  pins.  A 
beaker  or  other  vessel  containing  water  is  now 
placed  beneath  the  cylinder  and  raised  until  the 
cyclinder  is  sufficiently  immersed.  The  temperature 
of  the   muscle  is  altered  by  heating  or  cooling  this 


American  Journal  of  Physiology,  1904,  x,  p.  xliii. 


344  THE    OUTGO    OF    ENERGY 

water.  Direct  electrical  stimulation  of  the  muscle 
may  be  made  by  connecting  one  electrode  with  the 
metal  parts  of  the  apparatus  and  the  other  with  the 
copper  wire  attached  to  the  upper  end  of  the  muscle. 

Note  that  as  the  temperature  falls  the  contrac- 
tion curve  becomes  longer.  The  phase  of  rising 
energy  is  lengthened  more  than  the  relaxation. 
The  earlier  portion  of  the  relaxation  is  lengthened 
less  than  the  later ;  the  muscle  shows  a  tendency 
to  contracture  (see  page  340). 

Place  fresh  paper  on  the  drum.  Let  the  drum  re- 
volve very  slowly.  Place  a  lighted  Bunsen  burner 
under  the  arm  of  the  muscle  warmer.  At  intervals 
of  5°  stimulate  the  muscle  with  a  maximal  break 
current.     Note  the  changes  in  the  contraction. 

The  height  of  contraction  is  least  at  the  freezing 
point  of  the  muscle  (-5°).  It  rises  from  the 
freezing  point  to  0°;  falls  from  0°  to  19°;  in- 
creases to  30°,  which  is  the  maximum ;  from  30° 
to  45°  diminishes  again;  and  at  45°  the  frog's 
muscle  usually  enters  into  a  state  called  rigor 
caloris;  the  muscle  becomes  opaque,  inelastic, 
resistant  to  the  touch,  shortens  very  considerably, 
and  undergoes  chemical  changes  of  great  impor- 
tance. The  duration  of  contraction  lessens  with 
the  rising  temperature,  being  least  at  30°.  Above 
30°  the  duration  remains  approximately  un- 
changed.    The  latent  period  is  increased  at  low 


THE    CHANGE   IN    FORM  345 

temperatures,  diminished  at  high.  Above  30°  the 
excitability  to  electrical  stimuli  diminishes  stead- 
ily ;  it  disappears  almost  entirely  before  rigor  is 
reached. 

Influence  of  Veratrine  on  the  Form  of  the  Con- 
traction.—  With  a  capillary  pipette  inject  in  the 
dorsal  lymph  sac  5  drops  of  a  1  per  cent  solution 
of  veratrine  sulphate  or  acetate.  After  a  few 
minutes,  test  for  symptoms  of  veratrine  poisoning 
by  pinching  the  foot  from  time  to  time. 

Soon  the  mechanical  stimulation  will  be  fol- 
lowed by  prolonged  contraction  of  the  extensor 
muscles  and  still  more  prolonged  relaxation. 

Make  a  gastrocnemius  muscle  preparation. 
Fasten  the  muscle  to  a  muscle  lever  and  bring  the 
writing  point  against  a  smoked  drum.  Eecord  a 
single  contraction. 

Note  the  increased  height  of  the  phase  of 
shortening,  and  the  prodigious  increase  in  the 
duration  of  the  phase  of  relaxation.  This  con- 
tracture (page  340)  is  lessened  by  repeated  stimu- 
lation, but  reappears  if  the  muscle  be  allowed 
to  rest.  Cooling  or  warming  usually  causes  the 
veratrine  effect  to  disappear  temporarily. 

A  quick  initial  contraction  may  precede  the 
characteristic  veratrine  contraction,  possibly  be- 
cause the  veratrine  affects  differently  the  red  and 
the  clear  fibres. 


346  THE    OUTGO   OF   ENERGY 


Tetanus 

Superposition  of  Two  Contractions. —  Arrange 
a  gastrocnemius  muscle  to  write  on  a  smoked 
drum.  Connect  the  binding  posts  on  the  muscle 
lever  and  muscle  clamp  with  the  secondary  coil 
of  an  inductorium.  In  the  primary  circuit  (posts 
1  and  2)  place  the  electro-magnetic  signal  and  a 
simple  key.  Let  the  drum  revolve  at  a  rapid 
rate.  Send  two  maximal  induction  currents 
through  the  muscle  at  varying  intervals,  begin- 
ning with  the  shortest  interval  possible.  The 
secondary  should  be  at  such  a  distance  from 
the  primary  coil  that  both  make  and  break  cur- 
rents shall  cause  maximal  contraction. 

If  the  second  stimulus  fall  in  the  latent  period 
of  the  first  contraction,  the  stimulus  will  be  with- 
out effect.  If  the  second  stimulus  fall  between 
the  beginning  of  shortening  and  the  end  of  relax- 
ation caused  by  the  first  stimulus,  the  contraction 
following  the  second  stimulus  will  not  begin  from 
the  base  line,  but  will  be  superposed  on  the  first, 
as  if  the  state  of  shortening  from  which  the 
second  contraction  begins  were  the  resting  stage 
of  the  muscle.  The  height  readied  by  the 
second  contraction  will  be  greater  than  that 
reached   by    the  first.      The    summed  height  is 


THE   CHANGE   IN   FORM  347 

usually  greatest  when  the  second  contraction 
starts  from  the  summit  of  the  first,  but  this  rule 
is  not  invariable.  The  summit  of  the  summed 
contraction  does  not  necessarily  coincide  with  the 
summit  of  the  second  contraction  ;  the  higher  the 
summed  contraction,  the  quicker  the  summit  is 
reached. 

Superposition  in  Tetanus.  —  Place  the  vibrat- 
ing interrupter  (Fig.  50)  in  the  primary  circuit. 
Eepeat  the  preceding  experiment,  but  use  a  series 
of  stimuli  instead  of  only  two.  It  will  be  ob- 
served that  a  third  contraction  may  be  super- 
posed on  the  second,  a  fourth  on  the  third,  and 
so  on.  The  shortening  of  muscle,  however,  has  a 
limit ;  and  when  this  is  reached,  further  stimu- 
lation merely  maintains  this  maximum  degree  of 
shortening  until  fatigue  sets  in.  When  the  in- 
terval between  successive  stimuli  is  very  brief 
the  successive  contractions  appear  to  fuse  to- 
gether and  the  contraction  curve  becomes  a  con- 
tinuous line.  The  more  rapid  the  contraction, 
the  shorter  must  be  the  interval  between  succes- 
sive stimuli  in  order  to  cause  the  disappearance 
of  the  individual  contractions.  Thus  a  more 
rapid  rate  of  stimulation  is  necessary  to  produce 
complete  fusion  in  fresh,  highly  irritable  muscles 
than  in  those  the  irritability  of  which  has  been 
diminished  by  cold  or  fatigue.     For  this  reason 


348  THE   OUTGO   OF   ENERGY 

contractions  which  at  the  beginning  of  the  stim- 
ulation period  are  marked  by  notches  in  the  curve 
fuse  completely  as  longer  stimulation  brings  on 
fatigue.  Here  also  the  differences  in  the  structure 
of  muscles  already  mentioned  play  an  important 
part.  Thus  the  red  muscles  of  the  rabbit  are 
thrown  into  tetanus  by  a  much  smaller  number 
of  stimuli  per  second  than  are  the  more  quickly 
contracting  white  muscles. 

Relation  of  Shortening  in  a  Single  Contraction 
to  Shortening  in  Tetanus.  —  1.  Kecord  side  by 
side  the  contractions  of  a  muscle  unloaded  except 
by  the  muscle  lever.  Stimulate  with  a  single 
maximal  induction  current ;  stimulate  with  a 
brief  tetanizing  current. 

The  shortening  of  the  single  twitch  of  the  un- 
loaded muscle  is  as  great  as  the  shortening  in 
tetanus. 

2.  Load  the  muscle  with  ten  grams  and  repeat 
Experiment  1. 

The  shortening  in  tetanus  will  now  be  con- 
siderably greater  than  that  of  the  single  twitch. 

3.  Load  the  muscle  with  ten  grams  but  sup- 
port the  weight  by  the  after-loading  screw,  so 
that  the  weight  cannot  pull  on  the  muscle  until 
the  contraction  begins.  Record  one  contraction 
on  a  stationary  drum  in  response  to  a  maximal 
make    induction    current.     Turn    the   drum   one 


THE    CHANGE    IN    FORM  349 

millimetre.  Kaise  the  writing  point  of  the  lever 
one  millimetre  by  means  of  the  after-loading 
screw.  Stimulate  the  muscle  with  a  make  in- 
duction current  of  the  same  intensity  as  before. 
Again  turn  the  drum  and  raise  the  point  of  the 
lever  one  millimetre,  and  stimulate  the  muscle 
as  before.  Continue  this  until  the  after-loading 
screw  is  raised  so  high  that  the  muscle  no  longer 
shortens  sufficiently  to  raise  the  lever. 

Obviously  in  this  experiment  the  weight  is  arti- 
ficially supported  during  a  progressively  greater 
portion  of  the  contraction.  It  will  be  found  that 
the  total  shortening  of  the  muscle  loaded  only 
during  the  latter  portion  of  the  contraction  is 
as  great  as  the  shortening  of  a  loaded  muscle  in 
tetanus. 

The  Isometric  Method 

Thus  far  we  have  observed  the  development 
of  energy  in  a  muscle  stretched  by  a  small,  un- 
varying load.  The  principal  part  of  the  energy 
set  free  in  this  isotonic  process  appears  as  the 
mechanical  energy  of  a  visible  change  in  form ; 
a  small  part  of  the  energy  of  the  muscle  is  con- 
verted into  tension.  Fick  has  pointed  out  that 
if  the  muscle  be  made  to  pull  against  a  strong 
spring,  the  change  in  the  length  of  the  muscle 


350  THE    OUTGO    OF   ENERGY 

will  be  very  slight,  and  the  greater  portion  of  the 
energy  will  be  converted  into  tension  and  stored 
in  the  spring.  If  the  excursion  of  the  spring  be 
recorded  by  a  writing  lever,  the  curve  will  be 
practically  a  record  of  the  course  of  transforma- 
tion of  energy  into  tension,  and  will  be  only  to  a 
slight  extent  the  record  of  a  change  in  form. 

In  order  to  determine  the  amount  of  energy 
converted  into  tension  in  the  isometric  contrac- 
tion, it  is  necessary  to  graduate  the  spring  against 
which  the  muscle  pulls. 

Graduation  of  Isometric  Spring.  —  Attach  the 
large  scale-pan  to  the  strong  spring  of  the  appa- 
ratus shown  in  Fig.  60.  Place  a  long  straw  on 
the  end  of  the  spring.  Bring  the  writing  point 
against  the  smoked  paper  of  a  kymograph.  Turn 
the  drum  once  round  to  record  an  abscissa.  Re- 
turn the  drum  to  its  former  position,  and  place 
80  grams  in  the  scale-pan  attached  to  the  spring. 
When  the  spring  is  stretched  turn  the  drum  once 
round  to  record  the  bending  under  100  grams' 
weight.1  Restore  the  drum  to  its  former  posi- 
tion, add  100  grams,  and  make  record  of  the 
extension  at  200  grams.  Continue  the  record 
up  to  1000  grams.  Preserve  the  curve  for  ref- 
erence (page  363). 

i  The  scale-pan  weighs  about  20  grams. 


THE    CHANGE    IN    FORM 


351 


The  Heavy  Muscle 
Lever.1  —  It  is  sometimes 
necessary  to  after- load  a 
muscle  lever  with  weights 
far  in  excess  of  those  that 
a  light  muscle  lever  will 
bear  without  " springing" 
and  thus  altering  the  ab- 
scissa. Such  heavy  loads 
are  borne  by  the  heavy 
muscle  lever  illustrated  in 
Fig.  60.  A  tripod  of  ja- 
panned malleable  iron,  27 
cm.  high  and  17.5  cm. 
broad  at  the  base,  supports 
a  femur  clamp  and  a  mus- 
cle lever.  The  latter  is 
a  steel  tube  5  cm.  long, 
pierced  by  a  steel  axle  9  mm. 
long,  revolving  between 
heavy  brass  posts.  The 
lever  weighs  about  2.5  gms. 
The  aluminium  scale-pan 
weighs  about  20  gms.  ;  it 
holds  one  hundred  10-gram 
weights.  The  lever  may  be 
turned  completely  over  in 
a  backward   direction,  and 


Fig.   60.     The     heavy    muscle 
lever. 


1  American  Journal  of  Physiology,  1903,  viii,  p.  xl. 


352  THE    OUTGO    OF    ENERGY 

thus  be  entirely  out  of  the  way.  The  steel  spring 
shown  upon  the  left  of  Fig.  60  may  then  be  turned  to 
the  right  to  bring  its  wire  hook  into  the  opening 
through  which  the  scale-pan  is  reached.  The  scale- 
pan  may  then  be  attached  to  this  isometric  spring  and 
the  spring  empirically  graduated.  When  the  gradua- 
tion scale  has  been  written,  the  milled  screw  that 
holds  the  isometric  spring  upon  the  left-hand  post 
(Fig.  60)  may  be  loosened,  the  spring  turned  with  the 
hook  up,  and  the  screw  made  fast  again.  The  lower 
end  of  the  muscle  may  now  be  attached  to  the 
hook  upon  the  spring  and  an  isometric  curve  written. 

The  screw  clamp  holding  the  muscle  clamp  is 
insulated.  A  binding  post  upon  the  muscle  clamp, 
and  another  binding  post  upon  the  right-hand  post 
supporting  the  axle  of  the  lever,  allow  direct  stimula- 
tion of  the  muscle. 

This  lever  serves  especially  well  for  the  double 
abductor  preparation  of  Fick,  consisting  of  the  semi- 
membranosus and  gracilis  of  both  sides. 

Isometric  Contraction.  —  Invert  the  spring. 
Fasten  the  femur  of  a  gastrocnemius  preparation 
in  the  muscle  clamp,  and  the  Achilles  tendon  to 
the  spring.  Connect  the  binding  posts  on  the 
lever  and  the  clamp  with  the  secondary  coil  of  the 
inductorium,  arranged  for  single  maximal  induc- 
tion currents.  Let  the  drum  revolve  at  a  rapid 
speed.  Stimulate  the  muscle  with  a  maximal 
break  current. 


THE   CHANGE    IN    FORM  doo 

An  isometric  contraction  will  be  recorded. 

Eemove  the  spring,  and  attach  the  tendon  to 
the  lever  weighted  with  ten  grams.  Stimulate 
the  muscle  with  a  break  induction  current  of  the 
strength  used  before. 

The  usual  isotonic  curve  will  be  written. 
Comparison  of  the  isometric  and  isotonic  curves 
reveals  as  a  rule  in  the  isometric  curve  a  longer 
phase  of  rising  energy  and  a  flattened  summit 
or  plateau.  The  muscle  reaches  its  maximum 
tension  sooner  than  its  maximum  shortening  and 
maintains  the  maximum  tension  longer  than  the 
maximum  shortening. 

Contraction  of  Human  Muscle 

Simple  Contraction  or  Twitch.  —  Place  the 
middle,  ring,  and  little  fingers  in  the  support  of 
the  ergograph  (Fig.  61).  Let  the  adjustable  rod 
rest  on  the  index  finger  near  the  distal  end  of 
the  middle  phalanx.  Place  the  point  of  the  rod 
in  the  hole  nearest  the  free  end  of  the  spring. 
Adjust  the  writing  point  to  write  on  a  smoked 
drum  revolving  at  moderate  speed.  With  the  brass 
electrodes  covered  with  wet  cotton  (page  129), 
stimulate  the  abductor  indicis  with  a  single  max- 
imal break  induction  current.  Compare  the  form 
of  the  curve  thus  obtained  with  the  contraction 
curve  of  the  skeletal  muscle  of  the  frog. 

23 


°54 


OD- 


THE    OUTGO    OF    ENERGY 


The  Ergograph.1 — A  flat,  steel  spring  provided 
with  a  writing  point  is  fastened  in  a  stout  iron  support 
clamped  to  the  table  (Fig.  61).  The  second,  third,  and 
fourth  fingers  of  the  subject's  hand  are  fastened  with 
tapes  to  the  wooden  support.     Upon  the  index  finger 


C3CP= 


Fig.  61.     The  ergograph ;  also  employed  for  recording  the  isometric  and 
i si. tonic  contractions  of  human  muscle. 


near  the  distal  end  of  the  middle  phalanx  is  placed  a 
rod  the  length  of  which  is  adjustable.  The  point  of 
the  rod  passes  through  a  rubber  ring  and  presses 
against  the  under  side  of  the  spring.     When  the  point 

1  First  described  in  the  "  Introduction  to  Physiology,"  1901, 
p.  220. 


THE    CHANGE    IN   FORM  355 

is  near  the  free  end  of  the  spring,  contractions  of  the 
abductor  indicis  muscle  with  voluntary  and  electrical 
stimuli  may  be  recorded.  When  the  point  of  the 
rod  is  placed  near  the  cast-iron  support  of  the  spring, 
the  movements  of  the  spring  will  be  so  much  less  that 
almost  none  of  the  energy  of  the  muscle  will  be  con- 
verted into  mechanical  motion.  An  isometric  con- 
traction will  be  recorded. 

Isometric  Contraction.  —  Place  the  point  of  the 
adjustable  rod  in  the  hole  nearest  the  cast-iron 
support  of  the  spring.  The  movement  of  the 
spring  is  so  much  less  at  this  point  that  almost 
none  of  the  energy  of  the  muscle  will  be  con- 
verted into  mechanical  motion.  Stimulate  the 
muscle  as  before  with  a  maximal  break  induc- 
tion current.  Compare  the  isometric  curve  thus 
recorded  with  the  largely  isotonic  curve  previ- 
ously  obtained. 

Artificial  Tetanus.  —  Eeplace  the  adjustable  rod 
in  its  former  position  (isotonic  arrangement). 
Stimulate  the  abductor  with  the  tetanizing  cur- 
rent of  the  inductorium.  Compare  the  curve 
with  the  tetanus  of  frog  muscle. 

Natural  Tetanus.  —  1.  Contract  the  abductor 
by  voluntary  impulse.  This  also  gives  a  tetanus 
curve.  When  the  natural  tetanus  is  prolonged, 
it  frequently  is  marked  by  oscillations  having  a 
periodicity  of  about  ten  per  second. 


356  THE    OUTGO    OF   ENERGY 

2.  Place  the  adjustable  rod  in  the  hole  nearest 
the  iron  support  (isometric  arrangement).  Stimu- 
late the  muscle  (1)  with  the  tetanizing  current 
of  the  inductorium ;  (2)  by  voluntary  impulse. 

It  will  be  seen  that  the  energy  set  free  by  the 
natural  stimulus  is  much  greater  than  when  the 
muscle  is  stimulated  artificially. 

Smooth  Muscle 

Spontaneous  Contractions.  —  Make  two  cuts, 
5  mm.  apart,  through  the  frog's  stomach  at 
right  angles  to  the  long  axis.  Pass  a  bent  hook 
through  the  ring  (i.  e.  through  the  cavity  of  the 
stomach),  and  fasten  the  hook  in  the  muscle 
clamp.  Pass  a  second  hook  around  the  lower 
margin  of  the  ring  and  attach  it  by  means  of  a 
fine  copper  wire  to  the  straw  of  the  heart  lever 
(Fig.  53).  Contraction  of  the  circular  fibres,  can 
thus  be  made  visible.  Bring  the  writing  point 
against  a  drum  revolving  about  once  an  hour. 
Wrap  filter  paper  saturated  with  normal  saline 
solution  about  the  muscle  ring.  Keep  this 
thoroughly  moist.  Proceed  to  the  remaining  ex- 
periments, observing  the  stomach  preparation 
from  time  to  time. 

Spontaneous  rhythmic  contractions  will  appear. 
Note  the  changes  in  tonus. 


THE   CHANGE   IX   FOEM  357 

Simple  Contraction.  —  Prepare  a  second  ring 
of  frog's  stomach  in  the  manner  described  in 
the  preceding  experiment.  Attach  the  lower 
margin  of  the  ring  to  the  muscle  lever  by  means 
of  a  fine  copper  wire.  Carry  the  end  of  the 
copper  wire  to  the  binding  post  on  the  muscle 
lever.  Connect  this  post  and  the  post  on  the 
muscle  clamp  with  a  dry  cell,  interposing  a  sim- 
ple key.  Place  the  electro-magnetic  signal  in  the 
primary  circuit.  Bring  the  writing  points  of  the 
muscle  lever  and  the  signal  against  a  smoked 
drum  in  the  same  verticle  line.  Let  the  drum 
move  at  slow  speed.  Stimulate  the  muscle  by 
making  and  breaking  the  galvanic  current  once, 
not  oftener. 

Compare  the  duration  of  the  latent  period  with 
that  of  skeletal  muscle.  Compare  the  form  of 
the  contraction  curve  with  that  of  skeletal 
muscle. 

Tetanus.  —  Determine  how  frequent  the  stimuli 
must  be  in  order  that  the  separate  contractions 
may  be  fused  into  a  smooth  curve. 

Usually  the  muscle  after  contracting  loses  its 
irritability  for  several  minutes.  If  this  occur, 
the  ring  may  be  laid  aside,  covered  with  filter 
paper  saturated  with  normal  saline  solution. 
Excellent  curves  are  often  obtained  from  muscle 
preserved  in  this  way  for  halt"  an  hour  or  more. 


358  the  outgo  of  energy 

The  Work  Done 

Influence    of    Load    on    Work    done.  —  In     the 

tracings  obtained  in  the  experiments  on  page  341 
with  loads  of  10  grams  and  upwards  measure 
the  distance  from  the  summit  of  each  curve  to 
the  abscissa.  Calculate  the  gram-millimetres  of 
work   done    at    10,    30,    50,    70,  and   90   grams, 

using  the  formula  W= — in  which  W  is  work 
°  m 

done,  in  gram-millimetres ;  iv,  the  weight  lifted 

in  grams,  —  i.  e.  the  weight  of  the  scale-pan  and 

lever  (about  12  grams)  plus  the  weight  put  into 

the   scale-pan   (the   weight   of  the   muscle   itself 

may  be  neglected) ;  h,  the  height,  in  millimetres, 

to  which  the  load  is  lifted ;  m,  the  magnification 

of  the  lever. 

Write  the  results  on  the  smoked  paper. 

Note  that  within  wide  limits  an  increase  in  the 
load  increases  the  work  done  by  the  muscle. 

Absolute  Force  of  Muscle.  —  Secure  the  femur 
of  a  gastrocnemius  muscle  preparation  in  a  mus- 
cle clamp  and  fasten  the  tendon  to  the  rigid 
muscle  lever.  After-load  the  muscle  until  it 
just  fails  to  lift  the  load  when  stimulated  with 
tetanizing  induction  currents. 

The  load  which  neither  extends  a  contracting 
muscle  nor  allows  it  to  shorten  is  a  measure  of 
the  "absolute  force"  of  the  muscle. 


THE   CHANGE   IN   FORM 


359 


Total  Work  done ;   the  "Work  Adder  —  Attach 
a  scale-pan    to   the   cord    that   passes    over   the 
pulley    on    the    axle    of    the 
work  adder  (Fig.  62). 

The  Work  Adder.1  —  A  wheel 
of  aluminium  (Fig.  _G2)  bears 
upon  its  axle  a  counterpoised 
muscle  lever  ending  in  a  pawl 
through  which  the  wheel  is 
caused  to  revolve  when  the  lever 
is  pulled  upward  by  the  attached 
muscle.  A  second  pawl  pre- 
vents the  wheel  from  turning 
hack  when  the  muscle  relaxes. 
The  axle  of  the  aluminium  wheel 
bears  on  the  other  side  a  pulley, 
from  which  the  weight  is  sus- 
pended. The  turning  of  the 
wheel  winds  the  suspending  cord 
upon  the  pulley  and  thus  raises 
the  weight. 


Fig.  62.  The  work  ad- 
der ;  about  six-sevenths 
the  original  size.  The  han- 
dle is  not  shown.  The 
muscle  preparation  is  the 
double  abductor  suggested 
bv  Fick. 


Clamp     the     work    adder    to 

a  stand   in  such   a  way  that 

the  scale-pan  hangs  free  of  the  table.     Fasten  the 

tendon  of  the  gastrocnemius  muscle  preparation 


1  Introduction  to  Physiology,  1901,  p.  225.     The  first  work 
adder  was  devised  by  Fick. 


360  THE    OUTGO    OF   ENERGY 

to  the  lever  of  the  work  adder  at  a  distance  from 
the  axis  of  the  pulley  equal  to  the  radius  of  the 
pulley.  Connect  the  muscle  with  the  secondary 
coil  of  an  inductorium  arranged  for  single  maxi- 
mal  induction  currents.  Measure  the  distance  of 
the  pulley  weight  from  the  level  of  the  axis  of 
the  pulley.  Stimulate  the  muscle  with  induc- 
tion currents  at  intervals  of  one  second  until  the 
fatigued  muscle  ceases  to  contract.  (Stimulation 
may  be  made  by  opening  and  closing  a  simple 
key  in  the  primary  circuit  in  unison  with  the 
beat  of  a  metronome.) 

Measure  the  height  in  millimetres  to  which 
the  pulley  weight  has  been  lifted.  Multiply  this 
height  by  the  weight.  The  product  is  the  total 
work  done  in  gram-millimetres. 

Total  Work  done  estimated  by  Muscle  Curve.  — 
The  total  work  done  by  the  muscle  may  also  be 
estimated  by  measuring  in  millimetres  the  height 
of  each  successive  contraction  recorded  on  the 
smoked  paper,  adding  the  several  heights  together, 
dividing  the  sum  by  the  number  of  times  the 
distance  from  the  fulcrum  of  the  recording  lever 
to  the  point  of  attachment  of  the  muscle  is  con- 
tained in  the  distance  from  the  fulcrum  to  the 
writing  point,  and  multiplying  this  quotient  by 
the  sum  of  the  pulley  weight  plus  the  weight  of 
the  lever. 


THE    CHANGE   IN   FORM  Sbl 

In  tetanus  no  weight  is  raised  and  no  visible 
mechanical  work  is  performed.  That  internal 
work  is  performed  is  shown  by  the  rise  in 
temperature. 

Time  Relations  of  Developing  Energy.  —  The 
simple  muscle  curve  is  a  graphic  record  of  the 
mechanical  energy  set  free  by  the  muscle  in  lift- 
ing a  certain  load.  It  is  desirable  to  measure  the 
maximum  energy  that  the  muscle  can  set  free  at 
each  moment  from  the  beginning  of  contraction 
to  the  point  at  which  the  greatest  shortening  is 
reached. 

Place  the  electromagnetic  signal  in  the  primary 
circuit  of  an  inductorium  arranged  for  maximal 
make  induction  currents.  Arrange  a  tuning  fork 
to  write  on  a  smoked  drum  beneath  the  line 
drawn  by  the  writing  point  of  the  signal.  Fasten 
the  femur  of  a  gastrocnemius  muscle  in  the 
muscle  clamp  and  attach  the  tendon  to  the  heavy 
muscle  lever.  Place  the  three  writing  points  in 
the  same  vertical  line.  Connect  the  binding  posts 
on  the  muscle  clamp  and  the  lever  with  the  posts 
of  the  secondary  coil  of  the  inductorium.  "  After- 
load  "  the  muscle  with  50  grams.  Set  the  tuning 
fork  vibrating.  Spin  the  drum.  Stimulate  the 
muscle  with  a  single  maximal  make  induction 
current. 

The  muscle  will  not  shorten  until  the  energy 


362  THE    OUTGO   OF   ENERGY 

set  free  is  sufficient  to  lift  a  load  of  50  grams. 
Turn  the  drum  until  the  writing  point  of  the 
signal  rests  in  the  line  made  by  the  signal  when 
the  muscle  was  stimulated.  Let  the  drum  be 
stationary.  Set  the  tuning  fork  vibrating.  Its 
writing  point  will  mark  a  line  synchronous  with 
that  drawn  by  the  signal  during .  the  experiment. 
Eevolve  the  drum  a  little  farther,  until  the 
writing  point  of  the  muscle  lever  reaches  the 
point  at  which  contraction  began.  Set  the 
tuning  fork  vibrating  again.  Its  writing  point 
will  mark  a  line  synchronous  with  the  beginning 
of  contraction.  The  number  of  vibrations  in  the 
tuning  fork  curve  between  the  two  points  just 
recorded  is  the  interval  between  the  stimulation 
of  the  muscle  and  the  point  at  which  the  energy 
set  free  was  sufficient  to  move  a  load  of  50 
grams.     Note  this  interval. 

After-load  the  muscle  with  100,  150,  200,  250, 
and  300  grams,  and  repeat  the  above  experiment 
after  each  addition  of  50  grams. 

On  coordinate  paper  set  down  as  ordinates 
the  several  loads  employed  and  along  the  abscissa 
the  time  intervals  in  hundredths  of  a  second. 
Place  a  dot  at  the  junction  of  the  50-gram  line 
with  the  perpendicular  cutting  the  abscissa  at  the 
figure  indicating  the  interval  observed  between 
stimulation   and   the  moment  when   the  energy 


THE    CHANGE    IN   FORM  363 

developed  sufficed  to  raise  the  load.  Eepeat  this 
with  other  loads.  Join  the  dots.  The  resulting 
line  is  a  curve  showing  the  absolute  force  of  the 
muscle  at  successive  intervals  from  the  beginning 
to  the  end  of  the  phase  of  rising  energy. 

Eecord  with  this  same  muscle  an  isometric 
contraction  (page  350).  With  the  aid  of  the 
graduation  scale  of  the  isometric  spring  ascer- 
tain the  maximum  tension  developed  in  the 
isometric  contraction.  Compare  this  result  with 
that  secured  in  the  experiment  just  concluded 
on  the  time  relations  of  developing  energy. 

Elasticity  and  Extensibility 

Elasticity  and  Extensibility  of  a  Metal  Spring.  — 

Clamp  the  ergograph  (Fig.  61)  to  the  table  in 
such  a  way  that  the  writing  point  of  the  ergo- 
graph spring  shall  rest  against  a  smoked  drum. 
Attach  a  scale-pan  to  the  spring  near  the  free 
end.  Turn  the  drum  once  round  by  hand,  thus 
describing  an  abscissa  on  the  smoked  paper. 
With  the  forceps  place  2  ten-gram  weights  very 
carefully  on  the  scale-pan. 

The  spring  extends.  Turn  the  drum  2  mm. 
and  add  another  20  grams  to  the  scale-pan. 

A  further  extension  of  the  spring  will  be 
recorded. 


364  THE    OUTGO    OF    ENERGY 

Turn  the  drum  2  mm.  again.  Continue  to 
record  the  extension  of  the  spring  after  each 
addition  of  20  grams  until  a  load  of  200  grams 
has  been  reached. 

It  will  be  found  that  the  extension  curve  is  a 
straight  line.  The  extension  is  directly  propor- 
tional to  the  weights  employed. 

Eemove  the  weights  20  grams  at  a  time,  turn- 
ing the  drum  2  mm.  after  each  lightening. 

The  spring  will  return  to  its  former  length. 
Its  elasticity  (within  the  limits  of  extension  here 
used)  is  perfect. 

Of  a  Rubber  Band.  —  Place  the  muscle  clamp 
in  the  stand  of  the  heavy  muscle  lever  (Fig.  60). 
Secure  a  rubber  band  in  the  jaws  of  the  clamp 
and  fasten  the  other  end  of  the  band  to  the 
muscle  lever.  Eepeat  the  preceding  experi- 
ment, using  10-gram  loads  instead  of  20-gram 
loads. 

The  extension  curve  will  again  be  a  straight 
line.  The  return  to  the  original  length  will  not 
be  complete.  The  elasticity  of  the  rubber  band 
is  not  perfect.  An  "  extension  remainder "  is 
present.  After  a  considerable  time  the  exten- 
sion remainder  will  disappear  and  the  band  will 
return  to  its  former  length,  provided  the  exten- 
sion was  not  too  violent  nor  too  long-continued. 

Of  Skeletal  Muscle.  —  Isolate  in  both  limbs  the 


THE    CHANGE    IX    FORM  365 

mass  of  long,  parallel-fibred  muscles  extending 
along  the  inner  side  of  the  thigh  from  the  pelvis 
to  the  tibia.  Separate  from  the  remainder  of  the 
pelvis  the  portion  to  which  the  muscles  of  both 
sides  are  attached.  Eemove  the  muscles  of  both 
sides  together  with  the  part  of  the  tibia  and  the 
pelvis  in  which  they  are  inserted.  The  muscles 
of  the  two  sides  thus  form  practically  one  long 
muscle  held  together  in  the  middle  by  the  small 
piece  of  bone  into  which  they  both  are  inserted 
(Tick's  preparation,  Fig.  60). 

Eepeat  the  preceding  experiment,  using  this 
preparation  in  place  of  the  rubber  band. 

The  extension  curve  is  no  longer  a  straight 
line,  but  approximately  a  parabola.  In  organic 
bodies,  the  increase  in  length  is  not  proportional 
to  the  extending  weights,  but  grows  smaller  as 
the  weight  increases. 

A  perfectly  fresh  muscle  weighted  lightly  (e.  g. 
10  grams)  usually  returns  to  its  original  length 
when  the  extending  weight  is  removed.  With 
larger  weights,  the  return  is  not  at  first  com- 
plete :  an  extension  remainder  is  observed,  and 
the  original  length  is  reached  only  after  a  con- 
siderable time. 

Extensibility  increased  in  Tetanus.  —  With  the 
gastrocnemius  muscle  (unloaded  except  by  the 
writing  lever  and  scale-pan)  draw  an  abscissa  (1) 


•-> 


66  THE    OUTGO    OF    ENERGY 


with  the  muscle  at  rest;  (2)  with  the  muscle 
tetanized.  These  abscissae  record  the  length  of 
the  practically  unloaded  muscle  in  the  resting 
and  the  active  states.  Place  10  grams  in  the 
scale-pan  and  again  record  the  length  of  the 
muscle  (1)  at  rest ;  (2)  tetanized.  Make  similar 
records  for  each  10  grams  up  to  100. 

It  will  be  found  that  the  extension  curve  falls 
more  rapidly  in  the  active  than  in  the  rest- 
ing muscle;  the  extensibility  is  increased  in 
tetanus. 

Fatigue 

Skeletal  Muscle  of  Frog.  —  1.  Let  a  gastro- 
cnemius muscle  loaded  with  10  grams  write  its 
contractions  on  a  very  slowly  moving  drum. 
Connect  the  secondary  coil  with  the  binding- 
posts  on  the  muscle  clamp  and  the  muscle  lever. 
Stimulate  the  muscle  once  in  two  seconds  with  a 
maximal  induction  current,  using  make  and  break 
currents  alternately.  The  correct  interval  may  be 
obtained  by  listening  to  the  beat  of  a  metronome. 
Continue  to  record  the  contractions  until  the 
muscle  will  no  longer  shorten  when  stimulated 
(exhaustion). 

State  the  characteristic  features  of  the  fatigue 
curve. 

2.    With  a  fresh  muscle  repeat  the  stimulation 


THE    CHANGE   IN   FORM  367 

every  two  seconds  until  the  height  of  contraction 
has  diminished  about  one  half.  Now  record  the 
duration  of  the  latent  period,  phase  of  rising 
energy,  and  phase  of  sinking  energy  (page  334) 
on  a  rapidly  moving  drum. 

Note  the  absolute  and  relative  duration  of 
these  periods  as  compared  with  those  of  muscle 
not  fatigued. 

3.  Stimulate  a  sartorius  from  the  same  frog 
continuously  with  tetanizing  currents  and  record 
the  tetanus  curve. 

State  the  differences  between  the  fatigue  curve 
thus  secured  and  the  curve  obtained  by  less  fre- 
quent stimulation. 

Attention  has  already  been  called  to  the  dif- 
ferences which  depend  on  the  relative  proportion 
of  red  and  clear  fibres  (page  336).  The  latter 
are  more  easily  fatigued. 

Human  Skeletal  Muscle.  —  1.  Arrange  the  ergo 
graph  to  record  the  contractions  of  the  abductor 
indicis,  as  directed  on  page  353.  Place  the  point 
of  the  adjustable  rod  in  the  hole  nearest  the  free 
end  of  the  spring. 

Prepare  also  the  large  and  small  brass  elec- 
trodes for  artificial  stimulation  of  the  muscle  and 
place  them  in  position. 

Bring  the  writing  point  against  a  very  slowly 
moving  drum.     Contract  the  muscle  voluntarily 


368  THE    OUTGO    OF   ENERGY 

twice  every  second,  keeping  time  with  the  beat  of 
a  metronome,  until  two  hundred  contractions 
have  been  made. 

Now  stimulate  artificially  every  two  sec- 
onds, using  maximal  make  and  break  currents 
alternately,  until  two  hundred  contractions  have 
been  made. 

State  the  characteristics  of  the  twro  fatigue 
curves,  and  compare  the  curves  with  those 
obtained  from  frog's  skeletal  muscle. 

2.  From  a  fresh  subject  obtain  a  fatigue  curve 
by  artificial  stimulation  of  the  abductor  indicis, 
using  maximal  make  and  break  induction  cur- 
rents alternately  every  two  seconds,  as  directed 
in  the  preceding  experiment.  When  the  muscle 
has  been  stimulated  two  hundred  times,  contract 
it  voluntarily  every  two  seconds  until  two  hun- 
dred contractions  have  been  made. 

Compare  the  curves  with  those  obtained  in 
Experiment  1. 

Explain  these  paradoxes. 

It  has  been  pointed  out  on  page  357  that 
smooth  muscle  loses  its  irritability  much  more 
rapidly  than  striated  muscle. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Volume  tube,     ljuuseu  burner.     Inductorium.     Two  dry 


THE    CHANGE   IN    FORM  369 

cells.  Wires.  Muscle  clamp.  Fine  copper  wire.  One 
hundred  ten-gram  weights.  Muscle  lever.  Electro-mag- 
netic signal.  Kymograph.  Tuning  fork.  Cork  clamp. 
Four  needle  electrodes.  Pole-changer.  Pin.  Cork.  Two 
stands  with  clamps.  Ten  one-gram  weights.  Muscle- 
warmer.  Split  shot.  Ice.  One  per  cent  solution  of 
veratrine  acetate.  Wheel-interrupter.  Vibrating  reed. 
Straw  36  cm.  long  with-  platinum  contact.  Mercury  cup. 
Eigid  muscle  lever.  Spring  ergograph  with  rod.  Hand 
clamp.  Ergograph  clamp.  Large  weight  pan.  Cotton. 
Two  bent  hooks.  Heart-holder.  Filter  paper.  Simple 
key.  Work  adder.  Co-ordinate  paper.  Rubber  band. 
Metronome. 


370  THE    OUTGO   OF   ENERGY 


IV 


THE   CENTRAL  NERVOUS  SYSTEM 
Simple  Eeflex  Actions 

The  Spinal  Cord  a  Seat  of  Simple  Reflexes.  — - 
1.  By  means  of  a  hook  or  thread  passed  through 
the  lower  jaw  suspend  vertically  a  frog  the  brain 
of  which  has  been  destroyed  with  the  seeker  ;  the 
legs  must  not  touch  the  table.  Pinch  a  toe  with 
the  forceps. 

The  leg  will  be  drawn  up. 

A  stimulus  to  the  skin  has  caused  the  con- 
traction of  muscles.  The  afferent  impulse  set 
going  by  the  sensory  stimulus  is  changed  into 
a  motor  efferent  impulse.  This  is  an  example  of 
reflex  action. 

2.  Destroy  the  spinal  cord  with  the  seeker. 
Stimulate  the  skin  of  the  right  leg  electrically 
and  mechanically. 

In  no  case  will  the  sensory  stimulus  call  forth 
the  reflex  contraction  of  a  skeletal  muscle.  Yet 
the    nerves    coming    from    the    skin    and   going 


THE  CENTRAL  NERVOUS  SYSTEM      371 

to  the  muscles  are  still  intact.  Only  the  spinal 
cord  has  been  destroyed. 

The  conversion  of  sensory  into  motor  impulses 
for  skeletal  muscles  is  a  function  of  the  central 
nervous  system. 

Influence  of  Afferent  Impulses  on  Reflex  Action. — 
Destroy  the  brain  of  a  strong  frog  with  the  seeker. 
Gently  pinch  a  toe  of  the  right  foot. 

Only  the  right  leg  will  be  drawn  up. 

Pinch  a  toe  of  the  left  foot. 

Only  the  left  foot  will  be  drawn  up. 

Pinch  a  finger. 

Only  the  corresponding  arm  will  move. 

Pinch  the  whole  foot  sharply. 

More  extended  movements  will  be  made. 

The  character  and  location  of  the  stimulus 
affect  the  resulting  contraction. 

Threshold  Value  Lower  in  End  Organ  than  in 
Nerve-Trunk. — 1.  Carefully  expose  the  sciatic 
nerve.  Determine  the  least  strength  of  tetanizing 
current  that  will  cause  a  crossed  reflex  when 
applied  to  the  skin  of  the  foot.  Now  apply  the 
same  stimulus  to  the  trunk  of  the  nerve. 

As  a  rule,  the  intensity  required  to  produce 
reflex  action  is  less  when  the  stimulus  is  applied 
to  the  peripheral  endings  of  the  sensory  nerves 
than  when  the  nerve-trunks  are  stimulated. 


372  THE    OUTGO    OF    ENERGY 

2.  Divide  the  skin  over  the  back  in  the  median 
line.  Eaise  the  skin  on  one  side  until  the  small 
nerves  which  pass  across  the  dorsal  lymph  sac  to 
innervate  the  skin  come  into  view.  Sever  from 
the  surrounding  skin  a  piece  about  one  centi- 
metre square  containing  the  endings  of  one  of 
the  nerves.  Let  the  isolated  piece  with  its  nerve 
endings  remain  connected  with  the  body  only  by 
the  trunk  of  the  nerve.  As  before,  determine 
the  least  strength  of  tetanizing  current  that  will 
cause  a  reflex  movement  when  applied  to  the 
nerve-endings  in  the  skin  and  to  the  nerve-trunk 
respectively. 

The  threshold  value  for  reflex  action  will  again 
be  found  lower  in  the  nerve-endings  than  in  the 
nerve-trunk. 

Summation  of  Afferent  Impulses.  —  Pass  two 
fine  copper  wires  about  the  frog's  foot  a  centi- 
metre apart  and  connect  them  with  the  secondary 
coil.  Connect  the  primary  coil  through  a  simple 
key  with  a  dry  cell.  Stimulate  with  regularly 
repeated  make  induction  currents  of  such  strength 
that  single  stimuli  cause  no  reflex  contraction. 

Summation  of  the  subminimal  stimuli  will 
finally  cause  reflex  contraction. 

Determine  that  the  number  of  stimuli  neces- 
sary to  produce  a  reflex  becomes  smaller  when  (1) 


THE    CENTRAL    NERVOUS    SYSTEM  373 

the  strength  of  the  induction  currents  is  increased, 
and  (2)  when  the  interval  between  the  stimuli  is 
lessened. 

Segmental  Arrangement  of  Reflex  Apparatus.  — 
1.  Gently  pass  the  seeker  over  the  abdominal 
walls  on  one  side. 

The  muscles  in  that  region   only  will  twitch. 

Eepeat  the  stimulus,  but  use  a  stronger 
pressure. 

The  area  contracting  will  increase  in  extent 
approximately  in  proportion  to  the  increase  in 
the  stimulus.  The  afferent  nerves  from  any  one 
region  are  more  closely  related  to  the  efferent 
nerves  of  that  same  region  than  to  those  of  other 
regions.  The  fact  that  both  afferent  and  efferent 
fibres  spring  from  the  cord  at  the  same  level 
suggests  that  their  nerve  cells  lie  also  at  approxi- 
mately the  same  level.  On  increasing  the  stim- 
ulus the  afferent  impulse  spreads  from  segment 
to  segment  of  the  cord.  Further  evidence  of  the 
segmental  arrangement  will  be  gained  by  the 
following  experiment. 

2.  With  a  clean,  sharp  knife  make  transverse 
sections  of  the  spinal  cord,  beginning  in  the  cer- 
vical region.  A  short  time  after  each  section 
test  the  reflexes  from  the  hind  limb  by  mechani- 
cal stimulation. 


374  THE    OUTGO   OF   ENERGY 

Note  the  level  below  which  no  section  can  be 
made  without  rendering  the  reflex  impossible. 
The  nerve  cells  concerned  in  this  reflex  lie  on 
the  caudal  side  of  this  line. 

Now  in  a  second  frog  make  transverse  sections, 
beginning  at  the  caudal  end  of  the  cord,  and  test 
the  reflexes  as  before,  until  the  level  is  reached 
beyond  which  a  section  will  destroy  the  reflex. 

Observe  that  the  portion  of  the  cord  comprised 
between  the  two  levels  determined  forms  a  seg- 
ment which  contains  the  central  apparatus  con- 
cerned in  the  reflex  studied. 

Reflexes  in  Man.  —  1.  From  the  Skin.  —  Kub 
the  plantar  surface  of  the  foot  gently  with  some 
hard  object. 

The  foot  will  be  retracted  reflexly. 

Similar  results  may  be  obtained  by  rubbing 
the  skin  of  the  inside  of  the  thigh,  which  will 
cause  contraction  of  the  cremaster  muscles  ;  or  by 
rubbing  the  skin  of  the  abdomen,  which  will  be 
followed  by  contraction  of  the  abdominal  muscles. 

These  reflexes  are  of  importance  in  clinical 
diagnosis  because  by  means  of  them  the  seat  of  a 
diseased  area  in  the  central  nervous  system  may 
sometimes  be  defined,  since  the  reflex  depends  on 
the  integrity  of  the  corresponding  reflex  arc;. 

2.  Cornea  Refleto.  —  Touch  the  cornea  gently 
with  a  thread. 


THE  CENTRAL  NERVOUS  SYSTEM      375 

The  eye  will  be  closed  involuntarily. 

3.  Throat  Reflex.  —  Touch  the  posterior  wall 
of  the  throat. 

The  movements  of  swallowing  will  usually 
follow. 

4.  Piopil  Reflexes ;  Light  Reflex.  —  Close  one 
eye  for  several  seconds,  then  open  it  quickly. 

Note  the  contraction  of  the  pupil. 

5.  Consensual  Reflex.  —  Close  one  eye  as  before, 
but  watch  the  pupil  of  the  other  eye  when  the 
first  is  opened  again. 

The  pupil  wTill  contract. 

6.  Accommodation  Reflexes.  —  Look  alternately 
at  a  near  and  a  far  object.  The  pupil  will  con- 
tract when  the  eye  adjusts  itself  to  see  the  near 
object. 

Tendon  Eeflexes 

Knee  Jerk. — Sit  in  such  a  position  that  the 
knee  is  bent  at  a  right  angle,  and  the  foot  hangs 
free.  Let  an  assistant  strike  the  patellar  liga- 
ment with  the  side  of  the  hand. 

Note  the  sudden  contraction  of  the  extensors 
of  the  thigh,  the  so-called  knee  jerk. 

Flex  the  knee  at  different  angles  and  deter- 
mine in  which  position  the  resulting  contraction 
is  greatest. 

Knee  jerk  can  be  obtained  only  within  certain 
limits  of  extension. 


376  THE    OUTGO   OF    ENERGY 

Let  the  subject  immediately  before  the  stimu- 
lus is  applied  forcibly  contract  some  other  group 
of  muscles ;  clench  the  hand,  for  example. 

The  knee  jerk  is  reinforced. 

Ankle  Jerk.  —  Bend  the  foot  at  right  angles  to 
the  leg,  and  strike  the  tendo  Achillis.  The  ex- 
perimenter  should  hold  the  end  of  the  foot  in  his 
left  hand. 

Contraction  of  the  gastrocnemius  muscle  will 
be  observed. 

Gower's  Experiment.  —  Strike  the  side  of  the 
tendo  Achillis. 

A  contraction  will  result. 

Support  the  other  side  of  the  tendon  so  that 
the  gastrocnemius  muscle  will  not  be  stretched 
by  the  blow.     Eepeat  the  experiment. 

No  contraction  follows.  The  tendon  jerk  re- 
quires for  its  production  a  rapid  stretching  of  the 
muscles  involved  in  the  contraction. 

Try  to  obtain  tendon  jerks  from  other  muscles  ; 
for  example,  the  triceps  humeri,  flexors  of  hand, 
and  masseter  muscles. 

Normally  no  response  will  be  obtained. 

The  experiments  are  of  value  in  diagnosis  of 
diseases  of  the  central  nervous  system. 


the  central  nervous  system  377 

Effect  of  Strychnine  on  Eeflex  Action 

Inject  with  a  glass  pipette  a  few  drops  of  0.5 
per  cent  solution  of  sulphate  of  strychnine  into 
the  dorsal  lymph  sac  of  a  frog  the  brain  of  which 
has  been  destroyed  with  a  seeker. 

After  a  few  minutes,  very  weak  afferent- 
impulses  will  be  sufficient  to  call  forth  general 
spasmodic  reflex  actions.  Note  that  (1)  the 
strychnine  reflexes  are  paroxysmal,  (2)  the  mus- 
cles fall  into  more  or  less  prolonged  rigidity  (teta- 
nus), and  (3)  the  extensors  overcome  the  flexors, 
the  limbs  being  strongly  extended. 

The  characteristic  action  of  strychnine  is  evi- 
dently not  dependent   on  the  brain. 

Destroy  the  spinal  cord  with  a  seeker. 

Stimulation  of  muscles  and  nerves  will  not 
cause   spasmodic  contractions. 

Strychnine  acts  on  the  spinal  cord,  but  not  on 
the  muscles  or  the  peripheral  nerves. 

Complex  Co-ordinated  Eeflexes 

Removal  of  Cerebral  Hemispheres.  —  Place  a 
frog  under  a  glass  jar  containing  a  small  sponge 
wet  with  ether.  Be  very  careful  not  to  kill  the 
frog.  When  insensibility  is  complete,  place  the 
animal  on  a  frog-board.  Cut  through  the  skin  in 
the  median  line  of  the  skull,  from  the  nose  to  the 


378  THE    OUTGO    OF    ENERGY 

vertebral  column.  Connect  the  front  margins  of 
the  two  tympanic  membranes  by  a  transverse  in- 
cision through  the  skin.  This  transverse  line 
will  pass  over  the  junction  of  the  cerebral  lobes 
with  the  optic  lobes.  Strip  off  the  parietal  bones 
with  forceps,  beginning  at  the  anterior  end  oppo- 
site the  anterior  margin  of  the  orbit.  When  the 
cerebral  hemispheres  are  uncovered,  they  may  be 
removed  from  before  backwards.  Avoid  injuring 
the  optic  lobes.  Work  rapidly  but  carefully.  If 
the  ether  effect  diminish  before  the  operation  be 
finished,  replace  the  frog  under  the  glass  jar  for 
a  few  moments.  As  soon  as  the  hemispheres  are 
removed,  sew  up  the  wounds  in  the  skin. 

Note  the  signs  of  profound  inhibition. 

If  the  operation  be  done  carefully,  the  shock 
will  gradually  pass  away,  and  the  functions  possi- 
ble in  the  absence  of  the  cerebrum  may  then  be 
determined.  Put  the  frog  aside,  moistening  his 
skin  occasionally,  but  not  otherwise  disturbing 
him,  and  prepare  a  second  frog  for  the  experi- 
ment upon  the  "  croak  reflex  "  (page  o79).  When 
tli is  operation  is  completed,  resume  the  observa- 
tions on  the  first  frog,  while  the  second  frog  re- 
covers from  the  shock. 

1.  Posture,  etc.  — Write  down  the  differences 
between  the  frog  from  which  only  the  cerebral 
hemispheres  have  been    removed  and  a  frog  in 


THE    CENTRAL   NERVOUS    SYSTEM  379 

which  the  whole  brain  has  been  destroyed  with 
the  seeker,  in  respect  to  posture,  power  to  regain 
feet  when  laid  on  back,  respiratory  movements, 
position  of  eyelids,  leaping  and   swimming. 

2.  Balancing  Experiment.  —  Place  the  frog  on  a 
somewhat  roughened  board,  about  20  inches  long, 
8  inches  wide,  and  1  inch  thick.  Tilt  the 
board  gradually. 

The  frog  remains  motionless  until  his  centre 
of  gravity  is  disturbed.  He  then  moves  forward 
in  an  attempt  to  reach  a  stable  position.  By 
careful  management,  he  can  be  made  to  climb  up 
the  inclined  board,  perch  upon  the  narrow  edge, 
and,  the  board  still  turning,  descend  head-first  on 
the  opposite  side. 

3.  Retinal  Reflex.  —  Place  the  frog  deprived  of 
cerebral  hemispheres  in  front  of  a  bright  light  \ 
for  example,  an  incandescent  electric  lamp.  In- 
terpose some  object,  such  as  a  small  instrument 
case,  between  the  light  and  the  frog,  so  that  a 
strong  shadow  is  cast  upon  the  frog's  eyes. 
Stimulate  the  frog  by  pinching  the  skin  of  the 
back. 

The  frog  will  jump,  but  will  avoid  the  object 
which  casts  the  shadow. 

4.  Croak  Reflex.  —  Sever  the  large  hemispheres 
from  the  remainder  of  the  brain  of  another  frog 
by  passing  a  knife  through  the  cranium  to  the 


380  THE    OUTGO    OF    ENERGY 

base  of  the  skull  from  side  to  side  in  a  line  join- 
ing the  anterior  margins  of  the  tympanic  mem- 
branes. (Where  possible,  a  male  frog  should  be 
selected  for  this  experiment.  Males  may  be  rec- 
ognized by  the  cushion-like  thickening  on.  the 
innermost  digit  of  the  manus,  or  hand ;  the  male 
Eana  esculenta  possesses  bladder-like,  resonating 
pouches  connected  on  each  side  with  the  month 
cavity.)  After  the  immediate  shock  of  the  opera- 
tion has  passed,  stroke  the  back  over  the  anterior 
half  of  the  spinal  cord. 

Keflex  croaking  will  be  observed. 

The  croak  reflex  can  be  inhibited  by  simultane- 
ous pinching  of  one  of  the  limbs  or  other  strong 
stimulation.     (Compare  page  384.) 

If  the  experiments  on  the  frog  in  which  the 
cerebral  hemispheres  were  extirpated  were  not 
satisfactory,  repeat  them  on  this  frog  in  which 
the  hemispheres  were  simply  separated  from  the 
remainder  of  the  brain. 

These  observations  teach  that  very  complicated 
co-ordinated  actions  are  possible  in  the  absence 
of  the  large  hemispheres.  Only  simple  reflexes 
are  possible  when  the  whole  brain  is  removed. 
Consequently,  the  seat  of  these  complicated  re- 
flexes must  lie  in  the  brain  between  the  cord  and 
the  cerebral  hemispheres. 


the  central  nervous  system         381 

Apparent  Purpose  in  Eeflex  Action 

1.  Destroy  the  brain  of  a  frog  with  the  seeker. 
Dip  small  pieces  of  filter  paper  in  strong  acetic 
acid.  Remove  the  superfluous  acid,  lay  the 
paper  bearing  the  acid  on  (1)  the  frog's  thigh, 
(2)  the  foot,  (3)  the  back.  After  each  stimulation 
note  the  character  of  the  reflex  movement,  and 
then  carefully  wash  the  acid  from  the  skin. 

The  movements  are  related  to  the  areas  stimu- 
lated in  a  certain  purposeful  way.  Efforts  are 
made  apparently  to  brush  away  the  acid  paper. 

2.  Place  the  acid  on  the  flank  of  the  right  leg. 
Usually  the  leg  stimulated  strives  to  brush  away 
the  paper.     Hold  this  leg  fast. 

The  other  leg  (the  left)  will  be  used  to  re- 
move the  acid  from  the  opposite  limb.  (This 
experiment  succeeds  best  in  strong,  lively  frogs.) 

3.  Place  an  uninjured  frog  in  an  evaporating 
basin  containing  sufficient  water  to  immerse  the 
frog  to  the  neck  and  covered  with  wire  gauze 
to  keep  him  from  jumping  out.  Warm  the 
water. 

As  the  temperature  rises  to  from  20°-30°  C. 
the  frog  will  attempt  to  escape. 

Repeat  the  experiment  with  the  frog  the  brain 
of  which  has  been  destroyed. 

No    movements    of    escape    will    be    noticed. 


382  THE   OUTGO    OF   ENERGY 

About  35°,  muscular  twitchings  will  be  seen. 
At  38°-40°  death  takes  place  and  the  muscles 
become  rigid  (heat  rigor). 

This  observation  shows  that  volition  in  all 
probability  is  absent  in  the  brainless  frog.  It 
follows  that  reflex  actions  are  not  volitional; 
their  "  purpose  "  is  only  apparent. 

Keflex  and  Eeaction  Time 

Reflex  Time.  —  Destroy  the  brain  of  a  frog  with 
the  seeker.  Hold  one  leg  of  the  frog  aside  with 
the  glass  rod.  Bring  beneath  the  other  a  small 
beaker  almost  full  of  dilute  sulphuric  acid 
(2:1000).  Eaise  the  beaker  until  the  foot  is 
immersed  to  the  ankle.  Count  the  seconds  be- 
tween the  application  of  the  stimulus  (sulphuric 
acid)  and  the  withdrawal  of  the  foot. 

This  interval  is  the  reflex  time. 

Wash  the  foot  carefully  in  the  bowl  of  water. 

Reaction  Time.  —  Smoke  a  drum.  Eaise  the 
drum  off  its  friction  bearing  by  turning  the  screw 
at  the  top  of  the  shaft.  Place  the  writing  point 
of  an  electromagnetic  signal  against  the  smoked 
paper.  Arrange  a  tuning  fork  to  write  its  curve 
near  that  of  the  signal.  Connect  the  signal 
through  two  simple  keys  and  a  dry  cell  with  the 
primary  coil  of  an  inductorium  arranged  for 
maximal  single  induction  currents  (posts  1  and 


THE   CENTRAL   NERVOUS    SYSTEM  383 

2).  Let  stimulating  electrodes  pass  from  the 
secondary  coil  (bridge  up)  to  the  tongue  of  the 
subject.  Let  the  subject  hold  one  key  closed  un- 
til he  feels  the  stimulus  on  the  tongue. 

Direct  the  subject  to  shut  his  eyes.  Let  the  ob- 
server start  the  tuning  fork,  spin  the  drum,  and 
stimulate  the  subject  by  completing  the  primary 
circuit.  The  instant  the  subject  perceives  the 
stimulus,  he  will  break  the  circuit  by  releasing 
his  key.  By  means  of  the  tuning  fork  curve 
determine  the  interval  between  stimulation  and 
response.  This  interval  is  the  reaction  time  plus 
the  errors  of  observation  ;  for  example,  the  latent 
period  of  the  electromagnetic  signal.  Eepeat  the 
experiment  three  times  and  take  the  mean  of  the 
results. 

In  the  laboratory  note-book  make  a  list  of  the 
links  in  the  chain  between  stimulus  and  re- 
sponse, and  state  as  far  as  possible  the  errors  of 
observation. 

Reaction  Time  with  Choice.  —  Connect  the 
side  cups  of  a  pole-changer  (without  cross  wires) 
to  the  posts  of  the  secondary  coil.  Connect  one 
pair  of  end  cups  with  the  usual  stimulating  elec- 
trodes, the  other  pair  with  large  brass  electrodes 
covered  with  wet  cotton.  Let  the  ordinary  elec- 
trodes touch  the  forehead,  the  other  pair  the  hand 
of  the  subject.     The  other  connections  should  re- 


384  THE    OUTGO   OF   ENERGY 

main  as  before.  Eepeat  the  preceding  experi- 
ment but  tell  the  subject  to  signal  only  when 
the  tongue  (or  hand)  is  stimulated.  In  order  to 
do  this  he  must  add  to  his  former  reaction  a  de- 
cision as  to  the  part  stimulated. 

Eeaction  time  with  choice  is  longer  than  sim- 
ple reaction  time.  In  general,  the  more  compli- 
cated the  mental  processes  involved,  the  longer 
will  be  the  reaction  time. 

Inhibition  of  Eeflexes 

Through  Peripheral  Afferent  Nerves.  —  Expose 
the  left  sciatic  nerve  for  a  distance  of  about  15 
mm.  in  a  frog  the  brain  of  which  has  been  de- 
stroyed. Tie  a  thread  around  the  distal  end,  and 
sever  the  nerve  at  the  peripheral  side  of  the  liga- 
ture. Place  the  central  stump  of  the  nerve  on 
the  electrodes  of  the  inductorium,  the  short-cir- 
cuiting key  being  closed.  Make  the  primary 
circuit,  and  set  the  hammer  vibrating.  Now  open 
the  short-circuiting  key,  bring  the  right  foot  of 
the  frog  into  the  dilute  sulphuric  acid  up  to  the 
ankle,  and  count  the  seconds  from  the  moment 
of  immersion  to  the  moment  of  withdrawal,  con- 
tinuing meanwhile  the  stimulation  of  the  central 
end  of  the  left  sciatic  nerve. 

The  latent  period  will  be  much  prolonged. 

Wash  off  the  acid  carefully. 


THE  CENTKAL  NERVOUS  SYSTEM     385 

Keflex  actions  may  be  inhibited  by  the  simul- 
taneous stimulation  of  sensory  nerves. 

Through  Central  Afferent  Paths ;  the  Optic 
Lobes.  —  1.  Expose  the  brain  according  to  the 
directions  already  given  (page  377).  Immediately 
posterior  to  the  cerebral  hemispheres  lie  the  optic 
lobes,  two  gray  spherical  bodies.  Separate  the 
cerebral  hemispheres  from  the  optic  lobes  by  a 
transverse  incision,  and  carefully  remove  the 
hemispheres.  Wait  until  the  shock  of  the  opera- 
tion has  passed.  Now  suspend  the  frog  so  that 
the  tips  of  ,the  toes  hang  above  a  shallow  dish 
containing  water  made  strongly  sour  to  the  taste 
with  dilute  sulphuric  acid.  Determine  the  reflex 
time.  Wash  off  the  acid  and,  after  a  moment's 
rest,  sprinkle  a  very  little  finely  powdered  com- 
mon salt  on  the  cut  surface  of  the  optic  lobes. 
Again  determine  the  reflex  time. 

The  reflex  time  will  be  found  to  be  markedly 
increased  by  the  stimulation  of  the  optic  lobes. 

2.  Prepare  a  second  frog  in  the  same  manner. 
Determine  the  reflex  time.  Now  instead  of  stim- 
ulating the  optic  lobes,  remove  them,  and  again 
determine  the  reflex  time. 

The  removal  of  the  optic  lobes  shortens  the 
reflex  time. 

25 


386  the  outgo  of  energy 

The  Eoots  of  Spinal  Nerves 

Destroy  the  brain  of  a  strong,  large  frog  with 
a  seeker.  Divide  the  skin  over  the  vertebral 
colnmn  from  the  upper  end  of  the  urostyle  to 
the  level  of  the  fore  limbs.  Hook  back  the 
flaps  of  skin.  Remove  the  longitudinal  muscles 
on  either  side  of  the  spines  of  the  vertebrae,  thus 
exposing  the  bony  arches.  Saw  through  the 
arches  of  the  8th,  7th,  and  6th  vertebrae  (there 
are  ten  vertebrae  in  the  frog,  counting  the  uro- 
style) in  the  order  named.  Clear  away  the  bone 
and  the  underlying  tissues  until  the  last  three  or 
four  pairs  of  roots  shall  be  plainly  seen.  Grasp 
the  filum  terminale  and  cautiously  lift  the  cord 
until  the  spinal  nerve  roots  are  clearly  displayed. 

The  anterior  roots  are  hidden  by  the  large, 
superficial  posterior  roots.  The  conspicuous  pos- 
terior root  which  seems  to  be  the  last  is,  in  real- 
ity, the  9th,  the  next  to  the  last ;  the  last,  or 
10th,  is  smaller  and  lies  close  to  the  filum  termi- 
nale. Place  a  silk  ligature  about  the  middle 
of  an  anterior  and  a  posterior  root  on  the  right 
side.  With  single  induction  currents  as  stimuli 
ol  (serve  that  (1)  the  stimulation  of  only  the  cen- 
tral end  of  the  posterior  root  calls  forth  a  (re- 
flex) movement,  and  (2)  the  stimulation  of  only 
the  peripheral  segment  of  the  anterior  root  causes, 
movement. 


THE   CENTRAL   NERVOUS    SYSTEM  387 

On  this  same  side  cut  all  the  posterior  roots. 

No  stimulus  applied  to  the  right  leg  will  now 
discharge  a  reflex  action.  But  stimuli  applied  to 
sensory  nerves  elsewhere  may  still  cause  reflex 
movements  of  the  right  leg.  Motor  impulses  still 
pass  to  these  muscles.  But  only  the  anterior 
roots  remain. 

Hence  the  anterior  roots  of  spinal  nerves  trans- 
mit motor  impulses  from  the  spinal  cord  towards 
the  muscles  (efferent  impulses) ;  the  posterior 
roots  transmit  sensory  impulses  from  sensory  sur- 
faces towards  the  spinal  cord  (afferent  impulses.) 

Ludwig's  Demonstration.  — Destroy  the  brain 
of  a  large  frog  with  the  seeker.  Remove  the 
thoracic  and  abdominal  viscera,  taking  care  not 
to  injure  the  sciatic  nerve  plexus.  Remove  the 
7th  and  8th  vertebra?,  taking  the  greatest  pains 
not  to  injure  the  nerve  roots.  Divide  the  body 
transversely  at  this  level,  so  that  the  anterior 
and  posterior  halves  shall  remain  connected  only 
by  the  anterior  and  posterior  sciatic  roots.  Keep 
the   roots    moist    with    normal    saline    solution. 

Demonstrate  again  that  the  anterior  roots 
transmit  efferent,  and  the  posterior  roots  afferent 
impulses. 

Localization  of  Movements  at  Different  Levels  of 
the  Spinal  Cord.  —  Separate  the  three  roots  which 
form   the  sciatic    nerve.     After   tying  a  thread 


388  THE    OUTGO    OF   ENERGY 

about  each  root  sever  it  from  the  spinal  cord  by 
a  cut  on  the  proximal  side  of  the  thread.  Stimu- 
late each  nerve  with  a  very  weak  tetanizing  cur- 
rent. Note  the  different  results  obtained  from 
nerves  arising  at  different  levels  of  the  cord. 
Stimulation  of  the  most  anterior  root  causes 
marked  flexion  of  the  limb ;  stimulation  of  the 
middle  roots,  extension  and  internal  rotation ; 
and  of  the  most  posterior,  simple  extension. 

In  a  frog  whose  nerves  have  not  been  cut 
expose  the  spinal  cord  and  stimulate  it  at  differ- 
ent levels  in  both  directions  along  its  length. 
The  various  movements  of  the  hind  limbs  are 
localized  at  different  levels  of  the  cord. 

Distribution  of  Sensory  Spinal  Nerves 

Destroy  the  brain  of  a  large  frog  with  the 
seeker.  Expose  the  lower  half  of  the  spinal  cord 
by  the  method  already  described.  On  one  side 
cut  the  dorsal  sensory  root  of  the  8th  spinal  nerve 
and  on  the  other  cut  the  sensory  root  of  the  7th, 
9th,  and  10th.  After  the  section  of  each  root 
test  the  cutaneous  sensibility  of  the  limbs  by 
placing  upon  the  skin  small  pieces  of  filter  paper 
(two  mm.  square)  moistened,  not  dripping,  with 
0.2  per  cent  sulphuric  acid.  Make  a  map  of  the 
anaesthetic  areas  in  each  leg,  and  note  the  lack 
of  correspondence. 


THE   CENTRAL    NERVOUS    SYSTEM  389 

Many  skin  areas  are  supplied  by  fibres  from  at 
least  two  sensory  roots.  The  fields  of  distribution 
overlap. 

Muscular  Tonus 

Brondgeest's  Experiment.  —  Fasten  a  lightly 
etherized  frog  back  uppermost  on  the  frog-board. 

In  a  line  between  the  ilium  and  the  coccyx 
open  the  pelvic  cavity  by  cautiously  dividing  the 
skin,  fascia,  and  muscle.  Divide  the  sciatic  nerve 
roots  on  the  operated  side.  Pass  a  hook  or  thread 
through  the  jaw  and  hang  the  frog  up. 

Observe  that  the  limb  the  nerves  of  which 
have  been  cut  is  relaxed,  so  that  the  toes  hang 
lower  than  those  of  the  limb  which  still  retains 
its  connection  with  the  central  nervous  system. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Stand. 
Muscle  clamp.  Bent  hook.  Inductorium.  Dry  cell. 
Electrodes.  Large  brass  electrodes.  Cotton.  Key. 
Frog-board.  Fine  copper  wire.  One-half  per  cent  solu- 
tion of  strychnine  sulphate.  Glass  jar  with  ether  and 
sponge.  Balancing  board.  Strong  acetic  acid.  Filter 
paper.  Evaporating  basin.  Wire  gauze.  Bunsen  burner. 
Thermometer.  Dilute  sulphuric  acid  (0.2  per  cent). 
Beaker.  Kymograph.  Electro-magnetic  signal.  Tuning- 
fork.     Pole-changer.     Vertebral  saw. 


390  THE    OUTGO    OF    ENERGY 


V 

THE   SKIN 
Sensations  of  Temperature 

Hot  and  Cold  Spots. — With  a  lead-pencil  point 
carefully  explore  an  area  about  an  inch  square 
on  the  back  of  the  wrist  or  hand.  Mark  with 
black  ink  the  places  where  a  distinct  sensation  of 
cold  is  felt,  and  with  red  ink  those  where  the 
sensation  is  one  of  warmth. 

The  places  indicated  are  the  so-called  hot  and 
cold  spots. 

Outline.  —  Attempt  to  define  more  exactly  the 
outline  of  one  of  the  cold  spots. 

The  spots  are  of  irregular  shape,  —  blotches 
rather  than  points. 

Mechanical  Stimulation.  —  1.  Gently  tap  one 
end  of  a  small  wooden  rod  the  other  end  of  which 
is  placed  on  a  well-defined  cold  spot. 

The  mechanical  stimulation  of  the  cold  spot 
will  give  a  sensation  of  cold. 

2.    Stimulate  a  warm  spot  mechanically. 

Chemical  Stimulation.  —  Rub  a  menthol  pencil 
over  a  small  area  on  the  back  of  the  hand. 


THE    SKIN  391 

A  sensation  of  cold  will  be  perceived.  This  is 
due  to  chemical  irritation  of  the  cold  spots.  The 
temperature  of  the  area  does  not  fall. 

Electrical  Stimulation.  —  It  has  been  found  that 
the  stimulation  of  a  well-defined  cold  or  warm 
spot  with  moderately  strong  induced  currents 
causes  a  sensation  of  cold  or  warmth  respectively. 

Temperature  After-Sensation. — Stimulate  a  cold 
spot  mechanically  with  a  pencil  point.  Eemove 
the  point. 

The  sensation  of  cold  outlasts  the  stimulus. 

Balance  between  Loss  and  Gain  of  Heat.  —  Pro- 
vide three  beakers  of  water.  Heat  them  to  20°, 
30°,  and  40°  C,  respectively.  Place  a  finger  of 
one  hand  in  the  water  at  20°,  and  a  finger  of  the 
other  hand  in  the  water  at  40°.  After  the  re- 
spective sensations  of  cold  and  warmth  have 
disappeared,  place  both  the  fingers  in  the  water 
at  30°. 

The  finger  from  the  cold  water  will  seem  warm 
and  that  from  the  warm  water  cold.  The  tem- 
perature of  the  skin  equals  the  balance  between 
its  heat  loss  and  heat  gain.  When  this  tempera- 
ture is  raised  or  lowered,  the  warm  spots  or  cold 
spots  respectively  are  stimulated. 

Fatigue.  —  Provide  three  beakers  containing 
water  at  10°,  32°,  and  45°  C.  respectively.  Place 
a  finger  of  one  hand  in  the  beaker  at  32°,  and  a 


392  THE    OUTGO    OF    ENERGY 

finder   of  the  other  hand  in  the  beaker  at  45°. 

o 

After  45  seconds  place  both  fingers  in  the  water 
at  10°. 

The  finger  taken  from  the  water  at  32°  (which 
is  about  the  normal  temperature  of  the  hand)  will 
feel  colder  than  the  other  finger.  Extreme  tem- 
peratures of  heat  or  cold  fatigue  the  temperature 
spots. 

Relation  of  Stimulated  Area  to  Sensation. — In- 
sert a  finger  of  one  hand  in  a  beaker  of  warm  or 
cold  water.  Note  the  sensation.  Insert  a  finger 
of  the  other  hand  in  the  water. 

The  intensity  of  the  sensation  will  increase 
with  the  extent  of  the  surface  stimulated. 

Perception  of  Difference.  — Provide  two  beakers 
of  water,  one  at  30°,  the  other  slightly  warmer  or 
colder.  By  introducing  a  finger  first  into  the  one 
and  then  into  the  other,  and  varying  the  tem- 
perature of  the  water,  ascertain  how  small  a 
difference  in  temperature   can  be  detected. 

Usually  a  difference  of  0.5°  C.  is  easily  recog- 
nized. 

Relatively  Insensitive  Regions.  —  1.  Compare 
the  temperature  sensation  perceived  on  touching 
with  a  pencil  point  the  median  line  of  the  fore- 
head,  nose,  and  chin  with  that  perceived  on 
touching  the  skin  on  either  side  of  the  median 
line. 


THE    SKIN  393 

The  skin  in  the  median  line  of  the  body  is 
comparatively  insensitive  to  temperature  varia- 
tions. 

2.  Similarly  compare  the  mucous  membrane 
with  the  skin. 

The  mucous  membranes  are  much  less  sensitive 
than  the  skin. 

Sensations  of  Pressuee 

Pressure  Spots.  —  Explore  the  surface  of  the 
forearm  by  bringing  the  blunted  point  of  a  needle 
gently  in  touch  with  the  skin. 

At  certain  spots  a  distinct  sensation  of  contact 
will  be  perceived.  Other  spots  will  give  only 
dull  sensations.  Pressure,  like  heat  and  cold,  is 
appreciated  by  scattered  sense-organs  in  the  skin, 
not  by  diffuse  general  sensation. 

Note  the  relation  of  the  pressure  points  (1)  to 
the  hair  follicles,  and  (2)  to  the  warm  and  cold 
spots  mapped  out  in  previous  experiments. 

Threshold  Value.  —  Take  from  the  human  head 
several  straight,  strong  hairs.  Cement  each  to 
the  end  of  a  little  stick  of  soft  pine  to  serve  as 
a  handle.  Provide  a  special  lever,  made  as  fol- 
lows :  With  a  hot  pin  burn  a  small  hole  at  the 
middle  of  a  straw  about  25  cm.  in  length.  Pass  a 
needle  through  this  hole  into  a  cork  held  in  the 
muscle  clamp.     Press  the  free  end  of  the  hairs 


394  THE    OUTGO    OF   ENERGY 

against  different  parts  of  the  skin  of  the  hand, 
arm,  and  face.     Select  hairs  which  when  pressed 
against  the  skin  of  the  respective  regions  give  no 
sensation  of   pressure.     Shorten  the  hairs   until 
the  pressure  is  just  perceptible.    This  will  be  the 
"pressure   threshold."     Make  a  loop  in  a  short 
silk   thread   and  pass  the  loop  about   the  lever 
exactly  one  millimetre  from  the  axis.     Hang  on 
the  end  of  the  thread  a  light  bent  hook.     Coun- 
terpoise    the    lever    very    exactly,    so    that    the 
slightest  force  applied  to  the  end  of  the  straw 
will  raise  the  lever  from  the  after-loading  screw. 
By  counterpoising  in  this  way,  the  lever  becomes 
a  balance.     On   the  bent   hook   hang   a   ring   of 
German  silver  wire  weighing  one  decigram  (0.1 
gram).     Find  a  point  on  the  lever  100  mm.  from 
the  axis.     The  weight  of  one  decigram  suspended 
1  mm.  from  the  axis  of  the  lever  will  be  raised 
by   a  force  of  j^q   of  a  decigram,  equal  to   one 
milligram   (0.001   gram)   applied   100  mm.  from 
the   axis.     At   HO  mm.  from  the  axis,  0.1  gram, 
suspended  1  mm.  from  the  axis,  will  be  lifted  by 
a  force  of  -gjjr  gram  (0.002  grain).     Find  the  dis- 
tance from  the  axis  at  which  each  testing-hair, 
when   pressed  vertically  against  the  lever,  will 
just   fail   to  lift  the  lever;  in  other   words,  the 
point  at  which  the  pressure  will  be  just  sufficient 
to  bend  the  hair.      The  number  of  millimetres 


THE    SKIN  395 

between  this  point  and  the  axis  of  the  lever, 
multiplied  by  one-tenth,  will  give  the  bending 
pressure  of  the  hair  in  the  fraction  of  a  gram. 
Make  ten  observations  on  each  hair  and  mark  the 
mean  bending  value  on  the  wooden  handle. 

Touch  Discrimination.  —  1.  Close  the  eyes  and 
let  an  assistant  test  the  different  parts  of  the 
skin  of  the  hand,  arm,  and  face  for  discrimina- 
ting power.  For  each  test  separate  the  points  of 
the  aesthesiometer  until  they  can  be  felt  as  two 
(ordinary  drawing  dividers  or  compasses  can  be 
used  for  an  aesthesiometer). 

Record  your  results  in  millimetres  for  finger- 
tips, palm  of  hand,  back  of  ringers,  back  of  hand, 
back  of  wrist,  flexor  and  extensor  surfaces  of  fore- 
arm, forehead,  cheeks,  lips,  and  tongue. 

2.  Separate  the  points  of  the  aesthesiometer 
about  20  mm.,  and  draw  them  gently  side  by 
side  along  the  extensor  surface  of  the  forearm 
from  the  elbow  to  the  wrist.  Repeat  the  experi- 
ment on  the  flexor  surface.  Try  the  same  for 
the  cheek  and  lips,  beginning  near  the  ear  and 
drawing  the  points  so  that  one  shall  go  above 
and  the  other  below  the  mouth. 

Describe  the  sensation  in  each  case,  and  sug- 
gest an  explanation. 

Weber's  Law.  —  Place  the  hand  palm  upward 
in  a  comfortable   position   on   the  table.     Close 


396  THE   OUTGO   OF   ENERGY 

the  eyes.  Let  an  assistant  place  on  the  last 
phalanx  of  the  middle  and  index  fingers  a  small 
round  box  containing  ten  small  shot. 

When  the  subject  has  formed  a  clear  percep- 
tion of  the  weight,  let  an  assistant  add  or 
subtract  shot,  and  record  the  number  of  shot  cor- 
responding to  the  smallest  difference  in  weight 
perceived  by  the  subject  (whose  eyes  of  course 
should  be  kept  closed).  Kepeat  the  experiment 
with  20,  30,  40,  and  50  shot  in  the  box  respec- 
tively. Determine  in  each  instance  the  ratio  of 
the  number  of  shot  added  or  subtracted  to  the 
number  with  which  each  experiment  was  begun. 

This  ratio  will  be  approximately  constant. 
The  degree  of  stimulation  necessary  to  cause  the 
perception  of  difference  always  bears  the  same 
ratio  to  the  degree  of  stimulation  already  applied. 
Weber's  law  is  less  true  for  very  small  and  very 
large  weights  than  for  those  of  medium  value- 
It  is  a  general  law  and  holds  good  for  visual 
judgments,  etc. 

After-Sensation  of  Pressure.  —  Place  a  rubber 
band  about  the  head  and  allow  it  to  remain  for 
several  minutes. 

On  removing  the  band,  a  distinct  after-sensa- 
tion of  pressure  will  l)e  felt. 

Temperature  and  Pressure.  —  Place  oil  the  back 
of  the  hand  supported   on   tin;   table  a  coin   the 


THE    SKIN  397 

temperature  of  which  has  been  made  such  that 
it  feels  neither  warm  nor  cold.  Compare  the 
pressure  sensation  (apparent  weight)  of  this  "nor- 
mal" coin  with  that  of  similar  coins  warmed 
and  cooled. 

The  hot  or  cold  coin  will  seem  heavier  than 
the  "  normal "  coin  of  equal  weight. 

Touch  Illusion  ;  Aristotle's  Experiment.  —  Cross 
the  right  middle  finger  over  the  right  index  finger 
and  place  them  on  the  palm  of  the  left  hand. 
Place  a  small  shot  between  the  crossed  fingers  in 
such  a  way  that  it  shall  touch  the  ulnar  side  of 
the  middle  finger  and  the  radial  side  of  the  index 
finger.     Eoll  the  shot  in  the  palm  of  the  hand. 

A  sensation  of  two  objects  will  be  felt. 

Apparatus 

Black  and  red  ink.  Small  wooden  rod.  Menthol  pen- 
cil. Inductorium.  Dry  cell.  Electrodes.  Key.  Three 
beakers.  Stand.  Ring.  Wire  gauze.  Bunsen  burner. 
Thermometer.  Needle  with  blunted  point.  Muscle  lever. 
Gram  and  ten-gram  weights.  German  silver  ring  weigh- 
ing 0.1  gram.  Silk  thread.  Four  small  wooden  handles 
for  pressure-hairs.  Bent  hook.  Drawing  dividers  (as 
eesthesiometer).  Small  round  box  containing  at  least  50 
shot.     Rubber  band  large  enough  to  go  around  the  head. 


398  THE   OUTGO   OF   ENERGY 

VI 

GENERAL   SENSATIONS 
Tickle 

Irradiation.  —  Gently  touch  the  skin  near  one 
nostril  with  a  dry  camel' s-hair  brush. 

Note  (1)  the  strong  sensation  produced  by 
the  slight  stimulus ;  (2)  the  irradiation  beyond 
the  spot  stimulated. 

After  image.  —  Repeat  the  stimulus  of  the  pre- 
ceding experiment. 

Measure  in  seconds  the  time  during  which 
the  sensation  outlasts  the  stimulus  (after  image). 

Topography.  —  Test  the  tickle  sensation  at  vari- 
ous points  on  the  skin  of  the  face,  hands,  and 
forearms.  Determine  whether  the  sensation  is 
greatest  about  the  several  openings,  where  skin 
joins  mucous  or  serous  membranes ;  e.  g.,  the 
nostrils,  the  conjunctival  sac,  the  auditory  canal. 
Do  the  results  indicate  a  protective  mechanism  ? 

Summation.  —  In  one  of  the  sensitive  areas 
found  in  the  preceding  experiment  determine  the 
difference  between  the  response  to  a  single  stim- 
ulus and  to  successive  stimuli. 

Fatigue.  —  In  any  sensitive  area  determine  (1) 
the  quickness  with  which  the  apparatus  for  the 
sensation  of  tickle  is  fatigued;  (2)  the  duration 
of  fatigue. 


general  sensations  399 

Pain 

Threshold  Value.  —  Arrange  an  inductorium  for 
tetanizincj  currents.  Place  the  electrodes  on 
the  tip  of  the  tongue,  and  move  the  secondary 
toward  the  primary  coil  until  no  farther  move- 
ment can  be  made  without  causing  the  stimula- 
tion to  become  painful.  Determine  for  this 
region  and  for  others  of  the  mucous  membrane 
of  the  mouth  and  of  the  skin  what  distance  of 
the  secondary  coil  from  the  primary  separates  the 
stimulus  at  which  pain  is  just  perceived  from 
that  at  which  the  pain  is  distinct. 

Latent  Period.  —  In  several  individuals  measure 
approximately  the  interval  between  the  applica- 
tion of  the  stimulus  (single  break  shock)  and  the 
resulting  painful  sensation. 

Summation.  —  Determine  the  number  of  sub- 
minimal stimuli  necessary  to  produce  pain. 

Topography.  —  Map  upon  the  skin  of  the  face 
and  arm  the  areas  specially  sensitive  to  pain. 

Individual  Variation.  —  Compare  the  reactions 
of  several  individuals,  and  note  the  differences  in 
threshold  value,  latent  period,  summation,  and 
topography. 

Temperature  Stimuli.  —  Fill  two  bowls  or  large 
beakers  with  water  twenty-five  degrees  respec- 
tively, hotter  and  colder,  than  the  temperature 


400  THE    OUTGO    OF    ENERGY 

of  the  hand.  Determine  whether  the  increase 
or  the  corresponding  decrease  in  temperature  is 
the  more  painful  to  the  immersed  hand. 

Motor  Sensations 

Judgment  of  Weight.  —  Lift  the  same  weight 
twice,  at  first  very  slowly  and  then  quickly. 

The  weight  will  appear  lighter  when  raised 
quickly. 

Sensation  of  Effort.  —  "  Hold  the  finger  as  if  to 
pull  the  trigger  of  a  pistol.  Think  vigorously 
of  bending  the  finger,  but  do  not  bend  it. 

"  An  unmistakable  feeling  of  effort  results. 

"  Eepeat  the  experiment,  and  notice  that  the 
breath  is  involuntarily  held,  and  that  there  are 
tensions  in  other  muscles  than  those  that  would 
move  the  finger."     {Sanforcl.) 

Sensation  of  Motion.  —  Let  the  forearm  and 
hand  rest  upon  a  table.  Bring  the  four  fingers 
of  the  hand  together,  and  turn  the  hand  so  that 
it  shall  rest  upright  upon  the  ulnar  side  of  the 
little  finger.  Close  the  eyes.  Abduct  the  first 
finger. 

The  second,  third,  and  fourth  finger  will  seem 
to  move  in  a  direction  opposite  to  the  movement 
of  the  first. 


TASTE  401 

VII 

TASTE 

Threshold  Value.  —  Prepare  solutions  of  cane 
sugar  of  the  following  strengths  :  1  :  1000,  1  :  800, 
1  :  600,  1  :  400,  1  :  200,  1  :  100.  Take  half  a 
teaspoonful  of  the  weakest  solution  into  the 
mouth,  roll  it  upon  the  tongue,  and  swallow 
it.  Note  whether  a  sweet  taste  can  be  per- 
ceived. Einse  the  mouth  thoroughly.  Proceed 
with  solutions  of  increasing  strength  until  the 
sweet  taste  is  just  perceptible. 

Topography.  —  1.  Select  a  solution  of  sugar 
slightly  more  concentrated  than  that  just  per- 
ceived to  be  sweet.  With  a  small  camel's-hair 
brush  apply  this  solution  to  the  several  parts 
of  the  tongue  and  the  palate.  Determine  the 
regions  sensitive  to  taste.  The  mouth  must  be 
rinsed  frequently.  2.  Dry  the  upper  surface  of 
the  tongue  with  a  handkerchief.  With  a  finely 
pointed  camel's-hair  brush  apply  a  twenty  per 
cent  sugar  solution  to  the  individual  fungiform 
papillse  and  to  the  mucous  membrane  between 
them.  Determine  whether  only  the  papilke 
perceive  taste. 

Relation  of  Taste  to  Area  stimulated.  —  Swallow 
a  very  small  quantity  of  a  minimal  solution  of 
sugar,  as    determined   in    the  experiment    upon 

26 


402  THE    OUTGO    OF   ENERGY 

threshold  value.  Einse  the  mouth,  and  then 
swallow  a  much  larger  portion  of  the  solution. 

The  taste  will  be  perceived  more  strongly,  the 
larger  the  area  stimulated. 

Electrical  Stimulation.  —  1.  Connect  two  small 
zinc  electrodes  through  a  simple  key  to  a  battery 
of  four  dry  cells.  Apply  one  electrode  to  an  in- 
different region,  the  other  to  the  tongue.  Close 
the  key. 

Note  the  sour  taste  at  the  positive  pole  and 
the  alkaline  taste  at  the  negative. 


INTRODUCTION   TO    PHYSIOLOGICAL    OPTICS      403 


VIII 

INTRODUCTION   TO   PHYSIOLOGICAL 
OPTICS 

All  visible  objects  give  out  light,  either  of  their 
own  making,  like  the  sun,  or  that  which  comes 
from  some  external  source  and  falls  upon  their 
surfaces.  Bays  that  fall  upon  any  surface  may 
disappear  (absorption),  or  be  thrown  back  from 
the  surface  (reflection),  or,  if  the  body  be  trans- 
parent, pass  into  it,  in  which  case  they  are  often 
bent  from  their  course  (refraction). 

Eeflection  from  Plane  Mirrors 

Angles  of  Incidence  and  Reflection.  —  Place  in 
front  of  the  condenser  in  the  lantern  (Fig.  63) 
the  diaphragm  with  2  mm.  aperture.  Cover  the 
round  window  in  the  optical  box  with  the  plain 
glass  slide.  Kemove  the  cork  from  the  tin  cylin- 
der.    Put  a  piece  of  lighted  Japanese  incense  in 


404 


THE    OUTGO   OF   ENERGY 


INTRODUCTION   TO    PHYSIOLOGICAL    OPTICS      405 

the  hole  in  the  cork.  Put  back  the  cork.  Place 
the  incense-holder  in  the  optical  box  and  put  the 
glass  lid  on  the  box.  Arrange  the  lantern  to 
throw  a  beam  of  light  through  the  window  into 
the  box.  The  smoke  will  be  made  luminous  by 
the  light  so  that  the  path  of  the  rays  can  be  seen. 
Make  the  rays  parallel  by  pushing  in  the  draw- 
tube  holding  the  outer  projecting  lens  of  the 
lantern.  Set  the  plane  mirror  against  the  side 
of  the  box.  Let  the  rays  fall  obliquely  upon 
the  mirror.  Accurate  measurement  would  show 
(1)  that  the  incident  ray,  the  reflected  ray,  and 
the  perpendicular  to  the  point  of  incidence,  all 
lie  in  the  same  plane,  and  (2)  that  the  angle 
between  the  incident  ray  and  the  perpendicular 

—  angle  of  incidence  —  is  equal  to  the  angle 
between  the  perpendicular  and  the  reflected  ray 

—  angle  of  reflection  (Hero  of  Alexandria,  about 
100  B.  C). 

Reflection  from  Concave  Mirrors 

Principal  Focus.  —  1.  Place  the  concave  mirror 
(the  polished  inner  surface  of  the  segment  of  a 
sphere  of  5  cm.  radius)  at  right  angles  to  the 
pencil  of  parallel  rays. 

The  rays  will  be  reflected  to  a  point  2J  cm. 
from  the  mirror.1     This  point,  to  which  parallel 

1  Much  smoke  will  make  the  rays  less  visible.     The  incident 


406  THE    OUTGO    OF    ENERGY 

rays  are  converged,  is  the  principal  focus  of  the 
concave  mirror.  The  distance  between  the  prin- 
cipal focus  and  the  reflecting  surface  is  termed 
the  principal  focal  distance ;  it  is  one  half  the 
radius  of  curvature.  Accurate  measurement 
would  show  that  the  angle  between  the  incident 
ray  and  the  perpendicular,1  in  this  case  the  radius 
of  the  spherical  surface,  equals  the  angle  of 
reflection. 

2.  Take  the  mirror  from  the  box  and  set  it 
in  the  principal  axis  of  the  beam  coming  from 
the  lantern.  Replace  the  2  mm.  diaphragm  by 
the  diaphragm  with  L-shaped  aperture.  At  the 
principal  focus  of  the  concave  mirror  hold  the 
small  round  screen  with  slender  handle. 

The  inner  rays  of  the  beam  will  be  inter- 
cepted by  the  screen.  The  outer  rays  will  be 
reflected  from  the  mirror  and  an  inverted,  real 
image  of  the  L_-shaped  aperture  will  be  seen  upon 
the  screen.  The  image  will  be  smaller  than  the 
object.  When  the  distance  between  the  mirror 
and  the  object  is  less  than  the  radius  of  curvature 
but  greater  than  the  focal  distance,  the  image 
is  real,  inverted,  and  larger.  With  concave 
mirrors,  real  images  are  always  inverted. 

and  tin:  reflected  beam  may  be  compared  l>y  turning  the  mirror 
slightly,  so  that  they  lie  side  by  side. 

1  It  is  assumed  that  the  spherical  surface  is  composed  of  an 
infinite  number  of  plane  surfaces. 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS      407 

3.  Obtain  a  luminous  point  as  follows.  In- 
sert in  front  of  the  condenser  the  diaphragm  with 
2  mm.  aperture.  Place  the  glass  slide  over  the 
window  of  the  box.  Pull  out  the  draw-tube  to 
make  the  pencil  of  rays  convergent.  Throw  this 
convergent  pencil  into  the  box.  Determine  its 
focus  by  finding  the  place  at  which  a  clear  image 
of  the  aperture  of  the  diaphragm  is  formed  upon 
a  screen.  This  focus  will  serve  as  a  luminous 
point. 

After  converging  to  the  focus,  the  rays  will 
diverge  again.  Place  the  mirror  2.5  cm.  from  the 
luminous  point.  The  luminous  point  will  then 
lie  at  the  principal  focus  of  the  mirror.  Turn 
the  mirror  at  a  small  angle  with  the  axis  of  the 
pencil. 

The  reflected  rays  will  be  parallel. 

Conjugate  Foci.  —  1.  Place  the  mirror  at  a  dis- 
tance from  the  luminous  point  greater  than  the 
radius  of  curvature  of  the  mirror. 

The  diverging  incident  rays  will  be  reflected 
from  the  spherical  surface  to  a  point  between  the 
luminous  point  and  the  mirror.  At  this  point  a 
real  image  of  the  luminous  point  will  be  seen. 

The  point  from  which  the  rays  diverge,  and 
the  point  to  which  they  converge  by  reflection 
from  the  mirror  are  termed  conjugate  foci. 

2.    Draw  back  the  lantern   and  thus  increase 


408  THE    OUTGO    OF   ENERGY 

the  distance  between  the  luminous  point  and  the 
mirror. 

As  the  distance  between  the  luminous  point 
and  the  mirror  increases,  the  distance  between 
the  mirror  and  the  image  diminishes. 

Move  the  lantern  towards  the  optical  box,  and 
thus  bring  the  luminous  point  towards  the  mirror. 

As  the  distance  between  the  mirror  and  one 
conjugate  focus  diminishes,  the  distance  between 
the  mirror  and  the  other  conjugate  focus  in- 
creases. As  one  focus  approaches  the  mirror,  the 
other  recedes. 

3.  Place  the  mirror  5  cm.  from  the  luminous 
point.  The  luminous  point  is  now  at  the  centre 
of  the  sphere  of  which  the  reflecting  surface  is 
a  segment.  The  incident  rays  are  therefore  all 
radial,  i.  e.  perpendicular,  to  this  surface.  Con- 
sequently all  the  rays  will  be  reflected  to  the 
point  of  origin.  The  incident  and  the  reflected 
rays  will  coincide.  The  centre  of  the  reflecting 
surface  and  its  optical  image  will  also  coincide. 
The  conjugate  foci  coincide. 

Virtual  image.  — •  1.  Place  the  mirror  at  a 
distance  from  the  luminous  point  less  than  the 
principal  focal  distance. 

The  reflected  rays  will  diverge.  They  will 
appear  to  proceed  from  a  point  lying  behind  the 
mirror.      The   distance   between   this    unreal    or 


INTRODUCTION   TO    PHYSIOLOGICAL    OPTICS      409 

virtual  image  and  the  mirror  will  be  greater  than 
the  distance  between  the  mirror  and  the  lumi- 
nous point.  As  the  luminous  point  approaches 
the  mirror,  its  virtual  image  will  also  approach. 

2.  Hold  a  small  object  nearer  the  mirror  than 
its  principal  focal  distance. 

Note  that  the  image  is  virtual,  upright,  and 
larger  than  the  object. 

Construction  of  Image  from  Concave  Mirrors.  — 
Determine  by  construction  the  length  of  the 
image  of  an  arrow  2  cm.  long,  placed  10  cm;  from 
the  middle  point  of  a  concave  mirror  of  5  cm. 
radius  of  curvature. 

Draw  a  horizontal  line.  With  any  convenient 
point  on  this  line  as  a  centre  describe  an  arc 
of  5  cm.  radius,  that  shall  intersect  the  line. 
This  arc  will  be  the  section  of  a  concave  mirror. 
The  horizontal  line  will  be  the  principal  axis, 
and  the  intersection  of  the  principal  axis  and 
the  arc,  the  middle  point  of  the  mirror.  The 
principal  focus  of  the  mirror  will  lie  halfway 
between  the  centre  of  curvature  and  the  middle 
point.  At  right  angles  to  the  principal  axis 
and  10  cm.  from  the  middle  point  draw  a  vertical 
arrow  2  cm.  long.  Determine  first  the  position 
of  the  image  of  the  point  of  the  arrow.  Draw 
from  the  point  to  the  mirror  an  incident  ray 
parallel  to  the  principal  axis.     This  parallel  ray 


410  THE   OUTGO   OF   ENERGY 

will  be  reflected  through  the  principal  focus. 
Draw  a  second  incident  ray  from  the  arrow  point 
through  the  centre  of  curvature.  This  ray  will 
be  perpendicular  to  the  spherical  surface  and 
will  be  reflected  in  the  same  line.  The  inter- 
section of  these  two  reflected  rays  will  be  the 
image  of  the  point  of  the  arrow. 

Determine  in  like  manner  the  position  of  the 
image  of  the  other  end  of  the  arrow. 

Keflection  fkom  Convex  Mirrors 

The  laws  of  reflection  from  convex  mirrors 
may  be  deduced  from  those  already  stated  for 
concave  mirrors.  The  image  reflected  from  con- 
vex mirrors  is  virtual,  upright,  and  smaller  than 
the  object. 

Determine  by  construction  the  length  of  the 
image  of  an  arrow,  2  cm.  long,  placed  10  cm. 
from  the  middle  point  of  a  convex  mirror  of 
5  cm.  radius. 

Effraction 

1.  Place  the  diaphragm  of  2  mm.  aperture  in 
front  of  the  condenser.  Push  in  the  draw-tube  of 
the  lantern  until  a  beam  of  parallel  rays  enter 
the  box.  In  the  box  lay  the  square  glass  bottle 
on  its  side  upon   a  wooden  block   and   at  right 


INTRODUCTION    TO   PHYSIOLOGICAL    OPTICS      411 

angles  to  the  pencil  of  light.  Neglect  the  re- 
flected rays. 

Observe  that  the  incident  rays  pass  through 
the  bottle  and  its  contents,  and  are  not  bent  from 
their  course.  Light,  passing  from  one  medium 
into  another  of  different  density,  is  not  refracted, 
provided  the  course  of  the  ray  be  perpendicular 
to  the  surface  separating  the  media. 

2.  Turn  the  bottle  so  that  the  incident  ray 
shall  enter  it  at  an  angle. 

On  passing  from  the  air  into  the  denser 
medium  of  the  glass  and  the  contained  liquid, 
the  incident  ray  will  be  bent  from  its  course. 
On  passing  from  the  denser  medium  into  the  air 
again,  the  ray  will  once  more  be  bent  from  its 
path.  Imagine  a  perpendicular  erected  at  the 
points  of  incidence  and  emergence.  The  re- 
fracted ray  will  be  bent  toward  the  perpendicu- 
lar on  passing  into  the  denser  medium,  and  away 
from  the  perpendicular  on  leaving  the  denser 
medium. 

Turn  the  bottle  and  thus  alter  the  angle  be- 
tween the  incident  ray  and  the  perpendicular 
(angle  of  incidence). 

The  angle  between  the  refracted  ray  and  the 
perpendicular  (angle  of  refraction)  increases  with 
the  ancde  of  incidence.  Exact  measurements 
made   by    Snellius    and   Descartes,  about   1621, 


412  THE    OUTGO    OF   ENERGY 

showed  that  —  (1)  the  refracted  ray  lies  in  the 
same  plane  with  the  incident  ray  and  the  per- 
pendicular, and  (2)  the  sine  of  the  angle  of  in- 
cidence stands  in  an  unalterable  relation  to  the 
sine  of  the  angle  of  refraction. 

The  sine  of  the  angle  of  incidence  is  to  the 
sine  of  the  angle  of  refraction  as  the  velocity  of 
the  light  ray  in  the  first  medium  is  to  its  velocity 
in  the  second,  or  refracting  medium.  The  ratio 
of  the  velocity  of  light  in  a  vacuum  to  its  velocity 
in  any  medium  is  termed  the  index  of  refraction, 
or  refractive  power  of  that  medium.  If  the 
velocity  of  light  in  a  vacuum  he  taken  as  1,  that 
A  light  in  air  at  0°  temperature  and  760  mm. 
pressure,  will  be  0.9997,  a  difference  so  slight 
that  the  velocity  in  air  is  usually  taken  as  the 
unit.  The  law  of  refraction  is  commonly  ex- 
pressed as  follows :  Let  n  represent  the  index  of 
refraction,  a  the  angle  of  incidence,  and  b  the 
angle  of  refraction ;  then 

.     7  sin  a 

sin  a  =  ?i  sin  o,  or  n  =  — — r. 

sin  b 

As  a  rule,  the  physically  denser  medium  is 
also  optically  denser.  Thus  the  refractive  index 
for  the  Frauenhofer  line1  I),  on  passing  from  air 

1  White  light  is  composed  of  rays  of  different  refrangibility ; 
hence  the  use  in  such  measurements  of  pure  spectral  rays. 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS      413 

into  crown  glass,  of  which  spectacle  lenses  are 
made,  is  1.530;  into  flint  glass,  1.635;  into  water 
at  15°  C,  1.332. 

Refraction  by  Prisms 

A  refracting  medium  bounded  by  two  plane 
surfaces  not  parallel  is  termed  a  prism.  The 
planes  are  termed  the  refracting  surfaces.  The 
angle  which  they  make  with  each  other  is  termed 
the  refracting  angle  of  the  prism. 

1.  Place  a  prism  in  the  optical  box  in  the 
beam  of  parallel  rays.  The  beam  will  be  bent 
from  its  course  on  entering  and  on  leaving  the 
prism.  The  emerging  pencil  will  be  divergent, 
for  the  homogeneous  rays,  the  union  of  which 
produces  the  sensation  of  white  light,  are  not 
equally  refracted,  —  the  rays  towards  the  red  end 
of  the  spectrum  are  bent  less  strongly  than  those 
towards  the  violet  end,  the  order  being  red, 
orange,  yellow,  green,  blue,  violet. 

Construction  of  the  Path  of  a  Ray  passing  through 
a  Prism.  —  Draw  a  horizontal  line  5  cm.  in  length. 
Upon  this  line  construct  the  section  of  a  prism.1 

1  To  construct  the  section  of  a  jwism:  Let  the  horizon- 
tal line  be  the  base  of  the  prism.  Place  the  brass  leg  of  the 
drawing  compasses  at  one  end  of  the  base  line.  Draw  a  circle 
of  3  cm.  radius.  Place  the  brass  leg  at  the  other  end  of  the 
base  line  and  draw  a  circle  of  the  same  radius.  A  line  joining 
the  intersections  of  the  two  circles  will  be  perpendicular  to  the 


414  THE    OUTGO    OF    ENERGY 

Draw  with  ink  a  ray  incident  to  the  refract- 
ing surface.1  Find  the  sine  of  the  angle  of  in- 
cidence.2 For  the  Franenhofer  line  D  passing 
from  air  into  crown  glass  the  ratio  of  the  sine 
of  the  angle  of  incidence  an  to  the  sine  of  the 
angle  of  refraction  bn  is 

an  :  bn  \\  1.53  '.  1 

For  the  same  light  passing  from  crown  glass 
into  air  the  ratio  of  the  sine  of  the  angle  of  in- 
cidence to  the  sine  of  the  angle  of  refraction  is 
the  reciprocal  of  the  ratio  from  air  to  crown  glass 

an  °.  bn  '. '.  1  '.  1.53 

middle  of  the  base  line.  Let  a  point  on  this  perpendicular 
5  cm.  above  the  base  line  be  the  apex  of  the  section.  Join  the 
apex  with  the  ends  of  the  base  line.  Ink  the  boundarj'  lines  of 
the  cross-section  thus  obtained.  Erase  the  pencil  construction 
lines. 

1  For  convenience  let  the  incident  ray  come  from  the  pro- 
longed base  line  of  the  prism  10  cm.  from  the  nearest  refract- 
ing surface.  Let  the  point  of  incidence  —  the  point  at  which 
tin-  incident  ray  meets  the  refracting  surface  —  be  about  the 
middle  of  the  refracting  surface. 

2  To  find  the  sine:  With  the  point  of  incidence  as  a  centre 
draw  a  circle  of  convenient  radius  (2  cm.).  Construct  a  radius 
of  this  circle  perpendicular  to  the  refracting  surface  at  the  point 
of  incidence.  From  the  intersection  of  the  circle  with  the  in- 
cident ray  draw  a  line  perpendicular  to  the  radius  (a  line  drawn 
from  the  point  of  intersection  parallel  to  the  refracting  surface 
will  be  perpendicular  to  the  radius).  This  is  the  sinus  line  of 
the  angle.  The  ratio  of  this  line  to  the  radius  of  the  circle  is 
the  sine  of  the  incident  angle. 


INTRODUCTION   TO    PHYSIOLOGICAL    OPTICS      415 

Measure  the  length  of  the  sine  of  the  angle  of 

incidence  in   millimetres.     Suppose  that   an   in 

the   present   instance    is    13    mm.  Then    with 
equation   ( 1 ) 

1.53  :  1  : :  13  :  x 

x  =  8.5  mm.,  the  sine  of  the  angle  of  refraction. 

Find  on  the  construction  circle  within  the 
prism  a  point  8.5  mm.  in  a  perpendicular  line 
above  the  diameter  at  right  angles  to  the  refract- 
ing surface.  Continue  the  ray  through  this  point 
to  the  second  refracting  surface.  Ink  the  path 
of  the  ray  within  the  prism.  Erase  the  con- 
struction lines  within  the  prism,  but  leave  un- 
touched those  without  the  prism.  Find  the  sines 
of  the  angles  of  incidence  and  refraction  at  the 
second  refracting  surface.  Draw  with  ink  the 
path  of  the  emergent  ray.  Preserve  all  these 
construction  lines.  Write  the  equations  in  ink 
in  the  upper  left-hand  corner  of  the  paper,  and 
the  four  sines  in  the  upper  right-hand  corner. 

The  degree  to  which  light  is  refracted  on  pass- 
ing through  a  prism  depends  on  the  refracting 
power  of  the  substance  of  the  prism,  the  size  of 
the  refracting  angle,  and  the  size  of  the  angle  of 
incidence. 


416  THE    OUTGO    OF    ENERGY 


Effraction  by  Convex  Lenses 

Principal  Focus.  —  1.  Place  the  diaphragm  of 
2  mm.  aperture  in  the  lantern.  Throw  a  beam 
of  parallel  rajs  into  the  optical  box.  Place  the 
double  convex  lens  in  the  axis  of  the  beam  about 
5  cm.  from  the  window  of  the  box. 

The  parallel  rays  will  be  brought  to  their 
principal  focus  about  10  cm.  (4  inches)  from  the 
lens.  Note  the  increase  in  intensity  as  the  rays 
converge. 

Place  the  black  wooden  screen  at  this  point. 

A  real  image  of  the  luminous  aperture  of  the 
diaphragm  will  be  perceived. 

2.  Place  the  diaphragm  of  2  mm.  aperture  over 
the  window  of  the  box.  Direct  the  light  of  the 
lantern  upon  the  opening  in  the  diaphragm. 
From  the  illuminated  opening  rays  will  diverge 
in  all  directions.  Place  the  lens  10  cm.  from  this 
luminous  body,  so  that  it  shall  lie  in  the  princi- 
pal focus  of  the  lens. 

The  diverging  rays  will  be  rendered  parallel. 
Pays  diverging  from  the  principal  focus  are 
rendered  parallel  by  passing  through  a  convex 
lens. 

A  lens  may  be  regarded  as  an  infinite  series  of 
prisms.     In  a  convex  lens  the  refracting  angle 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS      417 

of  each  hypothetical  prism  is  directed  to  the 
periphery  of  the  lens.  As  the  periphery  is  ap- 
proached the  refracting  angles  increase,  and 
hence  refraction  increases.  The  increased  refrac- 
tion of  the  outer  rays  diverging  from  a  luminous 
point  compensates  in  part  for  their  greater  angle 
of  incidence,  and  hence  most  of  the  rays  converge 
approximately  to  the  same  focus. 

Estimation  of  Principal  Focal  Distance.  —  Re- 
move from  the  lantern  the  tubes  holding  the  projec- 
tion lenses.  Place  in  front  of  the  condensing  lens 
the  diaphragm  with  L-shaped  aperture  each  limb 
of  which  is  5  mm.  long  and  1  mm.  broad.  Place 
the  convex  lens  in  the  axis  of  the  pencil  emerg- 
ing from  the  illuminated  slit  and  at  a  distance 
from  it  a  little  greater  than  the  principal  focal  dis- 
tance as  determined  roughly  in  the  preceding  ex- 
periment. On  the  other  side  of  the  lens  place  a 
screen  at  such  a  distance  as  to  give  a  strongly 
enlarged  clear  picture  of  the  l_.     Measure 

I  =  the  length  of  one  limb  of  the  |_, 
L  =  the  length  of  its  image, 
A  =  the  distance  of  the  screen  from  the  lens, 
/  =  the  principal  focal  distance  of  the  lens, 

then1  f=ATTl 

1  This  formula  is  derived  as  follows  ;  Let  a  "be  the  distance 

27 


418  THE    OUTGO    OF   ENERGY 

The  principal  focal  distance  of  a  double  con- 
vex lens  is  approximately  equal  to  the  radius 
of  curvature. 

Conjugate  Foci.  —  Place  in  the  lantern  the  dia- 
phragm of  2  mm.  aperture.  Eemove  the  tubes 
holding  the  projecting  lenses.  Place  the  convex 
lens  against  the  window  of  the  optical  box. 
Place  the  black  screen  twice  the  focal  distance 
from  the  lens.  Move  back  the  lantern  until  a 
clear  image  of  the  luminous  aperture  appears 
on  the  screen. 

The  point  from  which  rays  passing  through 
a  lens  diverge,  and  the  point  to  which  they  con- 
verge, are  termed  conjugate  foci.  Measure  the 
distance  of  the  luminous  aperture  from  the  lens. 
It  will  be  found  to  be  twice  the  focal  distance. 
When  the  point  of  divergence  is  separated  from 
the  lens  by  twice  the  focal  distance,  the  point 
of  convergence  is  equally  distant  from  the  other 

of  the  object  from  the  principal  surface  of  the  lens  (see  page  46); 

then — -  +  —  =      .     The  relation  between  the  size  of  the  image 
A        a      f  to 

and  the  size  of  the  object    is  L  '.  I  '.'.  A  I  a;  then  -  =  -j-r, 
and,   by  substitution,—  =  —  -+-  —,   whence     f  =  A  - 


f       A        AV  J  L+l' 

Compared  with  the  thickness  of  the  lens,  the  distance  of  the 
object  from  the  lens  is  so  great  that  it  may  be  used  in  place  of 
the  unknown  distance  from  the  principal  surface  (Kohlrausch,: 
Leitfaden  der  praktischen  Physik,  1887,  p.  142). 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS      419 

side  of  the  lens,  —  the  conjugate  focal  distances 
are  equal. 

Move  the  lantern  farther  from  the  lens. 

The  conjugate  focus  will  approach  the  lens. 
As  one  conjugate  focus  recedes  the  other  ap- 
proaches the  lens. 

Virtual  image.  —  1.  Place  the  2  mm.  diaphragm 
over  the  window  of  the  optical  box.  Let  the  di- 
verging rays  pass  through  the  convex  lens  placed 
at  a  distance  from  the  lumiuous  point  less  than 
the  principal  focal  distance. 

After  passing  through  the  lens,  the  diverging 
rays  will  continue  to  diverge  though  the  degree 
of  divergence  will  be  less.  Prolonged  backwards, 
they  would  unite  in  a  virtual  image  on  the  same 
side  of  the  lens  as  the  luminous  object.  The 
virtual  image  is  farther  from  the  lens  than  the 
object,  is  never  inverted,  and  is  always  enlarged. 
(Compare  the  construction,  directions  for  which 
will  be  given  on  page  421.) 

2.  Look  through  the  convex  lens  at  printed 
words  placed  between  the  lens  and  its  principal 
focus. 

The  image  is  virtual  and  enlarged. 

Construction  of  Image  obtained  -with  Convex 
Lens.  —  The  line  which  joins  the  centres  of  curva- 
ture of  a  double  convex  lens  is  termed  the  prin- 
cipal axis  or  optical  axis.     In  every  lens  there 


420  THE    OUTGO    OF   ENERGY 

are  in  the  principal  axis  two  points  so  placed 
that  when  the  entering  ray  is  directed  toward 
the  first,  the  emergent  ray  will  appear  to  come 
from  the  second  in  a  direction  parallel  to  the 
entering  ray.  These  are  termed  nodal  points. 
In  ordinary  glass  lenses  the  distance  between  the 
two  nodal  points  is  about  one  third  the  thickness 
of  the  lens.  When  this  distance  is  so  small  that 
it  may  be  disregarded,  the  two  nodal  points  may 
be  assumed  to  meet  in  an  intermediate  point 
termed  the  optical  centre  (compare  page  444)  of  the 
lens.  A  ray  directed  to  the  optical  centre  is  not 
refracted  but  passes  through  the  lens  in  a  straight 
line.  The  position  and  size  of  an  image  formed 
by  a  lens  can  be  found  by  drawing  one  line  from 
each  extremity  of  the  object  through  the  optical 
centre,  and  another  from  each  extremity  parallel 
with  the  principal  axis  to  the  lens  and  thence 
through  the  principal  focus.  The  intersections 
of  these  lines  mark  the  position  of  the  image  and 
its  upper  and  lower  limit.  It  is  necessary  to 
remember  that  parallel  rays  are  refracted  through 
the  principal  focus  only  when  the  aperture  of  the 
lens  does  not  exceed  approximately  ten  degrees. 

Draw  a  horizontal  line  to  serve  as  the  principal 
axis.  Let  a  point  near  the  middle  of  the  line  be 
the  optical  centre  of  a  double  convex  lens  of  10° 
aperture  and  5  cm.  radius.     The  radius  of  curva- 


INTRODUCTION   TO   PHYSIOLOGICAL    OPTICS      421 

ture  being  5  cm.,  the  principal  focus  will  lie 
approximately  5  cm.  from  the  optical  centre. 
Draw  through  the  optical  centre  a  line  10  mm. 
long  at  right  angles  to  and  bisected  by  the  prin- 
cipal axis.  Connect  the  ends  of  this  line  with 
the  principal  focus.  The  angle  included  will 
be  approximately  10°.  The  vertical  line  will 
then  represent  a  double  convex  lens  of  10°  aper- 
ture, assumed  to  be  without  thickness  in  order 
that  the  nodal  points  may  coincide  with  the  opti- 
cal centre.  At  any  distance  greater  than  5  cm., 
draw  an  arrow  at  right  angles  to  and  bisected 
by  the  principal  axis.  The  height  of  the  arrow 
must  not  exceed  the  diameter  of  the  lens,  so 
that  rays  emitted  from  the  ends  of  the  arrow 
parallel  to  the  principal  axis  of  the  lens  shall 
pass  through  the  lens.  From  the  ends  of  the 
arrow  draw  to  the  lens  and  thence  through 
the  principal  focus  incident  rays  parallel  to  the 
principal  axis.  From  each  end  of  the  arrow 
draw  a  line  through  the  optical  centre  of  the 
lens. 

The  intersections  of  these  lines  mark  the  upper 
and  lower  limits  of  the  image.  Note  that  the 
image  is  real  and  inverted.  If  the  object  be  situ- 
ated at  twice  the  focal  distance  from  the  lens, 
the  image  will  be  the  size  of  the  object ;  if  at  less 
than  twice  the  focal  distance,  the  image  will  be 


422  THE    OUTGO    OF   ENERGY 

larger  than  the  object ;  if  at  more  than  twice  the 
focal  distance,  the  image  will  be  smaller  than  the 
object ;  finally,  if  the  object  be  situated  between 
the  principal  focus  and  the  lens,  the  image  will 
no  longer  be  real,  but  virtual  and  larger  than  the 
object,  as  mentioned  on  page  419. 

Eefraction  by  Concave  Lenses 

Place  the  diaphragm  with  2  mm.  aperture  in 
front  of  the  condenser.  Throw  a  pencil  of  paral- 
lel rays  into  the  box.  Let  the  rays  fall  upon  a 
concave  lens. 

The  parallel  rays  will  be  rendered  divergent. 

Look  through  the  concave  lens  at  printed 
words.  The  image  is  virtual,  upright,  and 
smaller  than  the  object.  It  is  nearer  the  lens 
than  the  object,  and  is  always  within  the  prin- 
cipal focal  distance. 

Kefraction  by  Segments  of  Cylinders 

1.  Place  the  diaphragm  with  2  mm.  aperture 
in  front  of  the  condenser.  Throw  a  pencil  of 
parallel  rnys  into  the  box.  Place  the  cylindrical 
lens  in  the  axis  of  the  pencil  in  such  a  position 
that  the  curvature  shall  be  from  side  to  side,  i.  e. 
in  the  horizontal  meridian. 


INTRODUCTION   TO    PHYSIOLOGICAL    OPTICS      423 

The  image  of  the  circular  aperture  in  the  dia- 
phragm will  be  a  vertical  line  with  blurred  con- 
vex ends. 

Turn  the  cylinder  so  that  the  curvature  shall 
be  in  the  vertical  meridian. 

The  imacre  will  be  a  horizontal  line  with 
blurred  convex  ends. 

2.  Place  the  diaphragm  with  horizontal  slit  in 
the  lantern.  Throw  parallel  rays  into  the  box. 
Place  the  cylinder  in  the  axis  of  the  pencil  with 
its  curvature  vertical. 

The  horizontal  line  is  a  fusion  of  illuminated 
points.  From  each  point  rays  diverge  in  all 
directions.  Those  passing  from  any  point  in 
vertical  planes  through  the  cylinder  convex  in 
its  vertical  meridians  will  be  focussed  by  the 
convex  surface  in  a  corresponding  point  in  the 
image.  The  overlapping  of  such  points  will  form 
a  horizontal  line  with  clear  upper  and  lower 
edge.  The  rays  passing  from  any  point  in  the 
illuminated  line  in  horizontal  planes  through 
the  cylinder  with  vertical  curvature  will  be 
refracted  by  plane  glass  surfaces  and  will  not 
come  to  a  point  but  will  form  a  faint  horizontal 
line.  The  overlapping  in  the  image  of  the 
bright  points  in  which  unite  the  rays  passing 
in  vertical  planes  and  the  faint  horizontal  lines 
formed  by  rays  passing  in  horizontal  planes  will 


424  THE   OUTGO   OF   ENERGY 

form  upon  the  screen  a  horizontal  line  with 
blurred  ends. 

Place  the  vertical  slit  in  front  of  the  con- 
denser. 

A  broad,  faint,  horizontal  line  with  blurred 
ends  will  be  observed.  Draw  a  diagram  illus- 
trating  the  formation  of  this  image. 

Turn  the  cylinder,  so  that  the  curvature  shall 
lie  in  the  horizontal  meridian. 

The  horizontal  rays  are  at  once  united  in  a 
narrow  sharply  defined  vertical  line  with  blurred 
ends. 

Eefraction  through  Combined  Convex  and 
Cylindrical  Lenses 

Thus  far  segments  of  perfect  spheres  or  cylin- 
ders have  been  considered  separately.  In  the 
eye  both  the  cornea  and  the  lens  are  frequently 
more  convex  in  one  meridian  than  in  another. 
Such  surfaces  can  be  obtained  by  combining  a 
convex   with  a  cylindrical  lens. 

1.  Place  the  diaphragm  of  2  mm.  aperture  in 
front  of  the  condenser.  Throw  parallel  rays 
into  the  box.  Place  the  convex  lens  in  the  axis 
of  the  pencil  next  the  window.  Keceive  the 
image  of  the  illuminated  aperture  upon  a  screen 
placed  at  the  principal  focus.  The  image  will  be 
a  well-defined  circle.     Place  the  cylindrical  lens 


INTRODUCTION   TO    PHYSIOLOGICAL   OPTICS      425 

as  close  as  possible  to  the  convex  lens.  Let  the 
curvature  of  the  cylinder  be  in  the  vertical 
meridian. 

The  circle  will  give  place  to  a  vertical  line. 

Move  the  screen  about  4  cm.  nearer  the  lenses. 

The  image  of  the  circle  will  now  be  a  horizon- 
tal line. 

Place  the  screen  half  way  between  the  nearer 
and  the  farther  focal  lines. 

The  image  will  be  circular.  At  other  points 
in  the  focal  interval  or  space  separating  the  two 
focal  lines  the  image  will  be  an  ellipse. 

2.  Hang  the  block  containing  the  cylindrical 
lens  on  the  end  of  the  draw-tube  of  the  lantern. 
Leave  the  convex  lens  in  its  former  position. 
Fill  the  box  with  smoke.  Let  the  curvature  of 
the  cylindrical  lens  be  in  the  vertical  meridian. 
Observe  the  pencil  of  rays. 

The  pencil  will  be  drawn  out  to  a  vertical  line 
at  the  farther  focus.  Seen  from  above  the  cross- 
section  of  this  line  will  be  a  bright  spot.  At  the 
nearer  focus  the  pencil  will  be  flattened  to  a 
horizontal  line. 

Eotate  the  cylinder  through  90°.  The  curva- 
ture will  now  be  in  the  horizontal  meridian. 
Watch  the  pencil  as  the  lens  turns. 

As  the  cylinder  revolves  the  contour  of  the 
pencil   will   change.      When    the    curvature    is 


426 


THE    OUTGO   OF   ENERGY 


finally  horizontal  the  nearer  focal  line  will  be 
vertical,  the  farther  focal  line  will  be  horizontal. 

Eotate  the  cylinder  through  45°. 

By  looking  at  the  pencil  first  from  one  side  of 
the  box  and  then  from  the  other,  the  focal  lines 
may  readily  be  seen  in  profile,  as  well  as  in 
cross-section. 

Aberration 

Spherical  Aberration  by  Reflection.  —  In  Fig. 
64  a  concave  mirror,  AB,  has  the  centre  of  curva- 
ture, C,  and  the  principal  focus,  F.  BE  is  one 
of  several  incident  parallel  rays.  CE  is  perpen- 
dicular to  the  point  of  incidence.  EF  is  the  ray 
reflected  from  E  to  the  principal  focus,  G  the 


Pig.  64. 


point  at  which   the   reflected  ray  cuts  the  axial 
line  CK.     DEWC  G,  therefore  ZGCE=CEB 


INTRODUCTION   TO    PHYSIOLOGICAL   OPTICS      427 

=  0  E G,  and  C  G  E  is  an  isosceles  triangle.  Then 
if  r  be  the  radius  and  x  the  angle  formed  by  the 
perpendicular   CE  with  the  axial  ray   C  G,   CG 

T 

= .     So  lon^  as  angle  x  is  small,  cosine  x 

2  cos  x  '  ° 

will  be  nearly  1.  C  G  will  then  be  nearly  one 
half  the  radius  OK.  Hence  incident  rays  near 
the  axial  ray  CiT  will  be  reflected  approximately 
to  the  principal  focus  F,  which  lies  half  way 
between  the  centre  of  curvature  and  the  mirror. 
As  the  aperture  2  of  the  mirror  increases,  angle  x 
also  increases.  The  larger  x,  the  smaller  will  be 
the  denominator  of  the  expression  for  C  G,  and  the 
greater  the  distance  of  G  from  C.  Bays  reflected 
from  the  outer  portion  of  a  mirror  of  larger  aper- 
ture meet  the  principal  axis  nearer  the  mirror 
than  those  reflected  from  the  central  portion. 
The  intersection  of  the  reflected  rays  produces  a 
curved  line  —  the  caustic  curve  or  focal  line.  By 
revolving  Fig.  2  about  the  axis  C  K,  a  caustic  or 
focal  surface  will  be  obtained.2 

Spherical  Aberration  by  Refraction. —  1.  The 
observations  just  made  concerning  concave  mir- 
rors are  applicable  also  to  lenses.     Bays  entering 


1  The  aperture  is  the  angle   included  between  lines  drawn 
from  the  principal  focus  to  the  margins  of  the  mirror  or  lens. 

2  Jochmann   and    Hermes.      Grundriss   der   Experimental- 
physik,  1890,  p.  153. 


428  THE    OUTGO   OF   ENERGY 

a  lens  with  aperture  greater  than  10°  are  not 
refracted  to  the  principal  focus  but  cross  the 
principal  axis  between  the  principal  focus  and 
the  lens.  The  caustic  surface  formed  by  the 
intersection  of  these  peripheral  rays  may  readily 
be  shown  with  any  lens  or  cylinder  of  small 
radius  of  curvature. 

2.  Place  the  diaphragm  with  2  mm.  aperture 
in  front  of  the  condenser.  Throw  parallel  rays 
into  the  optical  box.  Set  in  the  box  near  the 
window  the  cylindrical  bottle  of  clear  glass  filled 
with  water.  The  bottle  will  serve  as  a  powerful 
refracting  cylinder. 

The  circular  pencil  of  parallel  rays  will  be 
brought  to  a  focus  in  a  vertical  line  (compare 
page  422).  The  outer  rays  of  the  pencil  pass 
through  the  outer  portion  of  the  cylinder,  and 
are  therefore  more  strongly  refracted  than  those 
near  the  optical  axis.  Each  refracted  ray  inter- 
sects the  refracted  rays  nearer  than  itself  to  the 
principal  axis.  These  intersections  form  two 
curved  surfaces  extending  from  the  principal 
focus  —  in  this  case  a  vertical  line  —  towards 
the  cylinder.  On  regarding  these  surfaces  from 
above,  their  curvature  will  be  apparent. 

3.  Remove  the  projecting  lenses;  place  the 
ground  glass  plate  and  the  diaphragm  with  2  mm. 
aperture  in  front  of  the  condenser.     Let  the  rays 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS      429 

diverging    from    the    illuminated    aperture    pass 
through  the  refracting  cylinder. 

The  curvature  of  the  caustic  surfaces  will  be 
more  noticeable  than  in  Experiment  2. 

Dispersion  Circles.  —  1.  Let  the  parallel  rays 
pass  through  the  double  convex  lens.  Place  a 
screen  at  the  principal  focus.  A  clear  image  of 
the  circular  aperture  in  the  diaphragm  will  be 
seen.  Move  the  screen  away  from  and  then 
towards  the  lens. 

When  the  screen  is  either  nearer  or  farther 
from  the  lens  than  the  principal  focus,  the  image 
will  be  larger  and  less  distinct.  The  screen  will 
cut  the  pencil  in  the  one  case  before  it  has  con- 
verged to  the  focus,  and  in  the  other  case  after 
it  has  passed  the  focal  point  and  is  diverging. 
Under  such  circumstances  the  image  of  a  point 
becomes  a  circle,  termed  a  dispersion  circle  or 
circle  of  confusion. 

2.  Substitute  the  diaphragm  with  L-shaped 
aperture  for  that  with  circular  aperture.  Place 
the  screen  a  little  nearer  or  farther  than  the 
focal  point. 

The  image  will  be  a  broad  blurred  line  with 
convex  ends.  The  pencils  proceeding  from  each 
luminous  point  in  the  line  will  fall  upon  the 
screen  in  dispersion  circles.  The  broad  line  is 
caused  by  the  overlapping  of  the  dispersion  cir- 


430  THE   OUTGO    OF    ENERGY 

cles.  Similar  blurring  by  dispersion  circles  is 
caused  by  the  rays  which  pass  through  the  outer 
parts  of  a  lens  coming  to  a  focus  sooner  than 
the  axial  rays. 

Myopia.  —  In  the  normal  eye  at  rest  parallel 
rays  are  brought  to  a  focus  upon  the  retina.  In 
the  myopic  eye  parallel  rays,  and  even  rays  to  a 
certain  degree  divergent,  are  brought  to  a  focus 
in  the  vitreous,  whence  they  fall  in  dispersion 
circles  on  the  retina.  The  most  common  cause 
of  myopia  is  the  abnormal  length  of  the  antero- 
posterior diameter  of  the  eye.  The  defect  can  be 
remedied  by  placing  a  concave  lens  before  the 
eye.  The  entering  rays  are  thereby  rendered 
divergent,  or  their  divergence  is  increased,  so  that 
their  focus  is  displaced  backwards  towards  the 
retina.  The  degree  of  the  myopia  is  measured 
by  the  strength  of  the  concave  lens  which,  placed 
before  the  eye,  will  bring  the  principal  focus 
exactly  to  the  retina. 

Let  parallel  rays  pass  through  the  convex  lens 
of  10  cm.  (4  inch)  focal  distance  placed  against 
the  window  of  the  optical  box.  Find  the  prin- 
cipal focus  and  then  move  the  screen  2.5  cm. 
farther  from  the  lens. 

The  image  will  be  blurred.  The  screen  will 
intersect  the  rays  diverging  from  the  focal  point. 

Hold  the  weak  concave  lens,  marked  —  2,  in 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS      431 

front  of  the  window.  This  lens  has  a  focal  dis- 
tance of  two  dioptres  or  one-half  metre  (see 
page  435). 

The  image  will  be  clear  again.  The  myopia 
in  this  case  is  therefore  —2D. 

Hypermetropia.  —  In  the  hypermetropic  eye  at 
rest  parallel  rays  and  even  those  to  a  certain 
degree  convergent  meet  the  retina  before  they 
have  come  to  a  focus.  The  most  frequent  cause 
of  hypermetropia  is  the  abnormal  shortness  of  the 
antero-posterior  diameter  of  the  eye.  The  defect 
can  be  remedied  by  placing  a  convex  lens  before 
the  eye.  The  entering  rays  are  thereby  rendered 
convergent,  or  their  convergence  is  increased. 
The  degree  of  the  hypermetropia  is  measured 
by  the  strength  of  the  convex  lens  which,  placed 
before  the  eye,  will  so  increase  its  convergent 
power  that  parallel  rays  will  come  to  a  focus  on 
the  retina. 

Place  the  screen  2.5  cm.  nearer  the  lens  than 
the  principal  focus. 

The  image  will  be  blurred.  The  screen  will 
intersect  the  rays  before  they  have  converged 
to  the  focal  point. 

Hold  the  weak  convex  lens,  marked  +  2,  in 
front  of  the-  window. 

The  image  will  be  clear.  The  hypermetropia 
in  this  case  is  therefore  4-2D. 


432  THE   OUTGO    OF    ENERGY 

Myopia  and  hypermetropia  will  be  further 
considered  under  refraction  in  the  eye. 

Chromatic  Aberration.  —  The  velocity  of  the 
homogeneous  spectral  rays  composing  white  light 
is  believed  to  be  the  same  in  a  vacuum  and  in 
gases,  but  differs  in  transparent  liquids  and  solids. 
The  front  of  the  light  wave  strikes  the  refracting 
surface  obliquely.  As  the  wave  front  enters  the 
medium,  its  speed  lessens.  Thus  the  part  of  the 
front  which  enters  first  travels  in  the  refracting 
medium  at  a  speed  less  than  the  remainder  which 
has  not  yet  entered.  The  wave  front  is  therefore 
bent  towards  the  retarded  portion.  The  shorter 
the  wave  length,  i.  e.  the  greater  the  wave  num- 
ber, the  slower  will  the  wave  advance  in  the 
refracting  medium.  Hence  the  wave  front  of  the 
violet  ray  moves  more  slowly  in  the  medium 
than  the  front  of  the  red  ray,  and  is  therefore 
bent  more  from  its  course.  The  reverse  of  this 
process  takes  place  when  the  wave  emerges  from 
the  refracting  medium.  The  violet  rays  are  there- 
fore more  refrangible  than  the  red,  and  on  enter- 
ing a  refracting  medium  pursue  a  different  path. 
Thus  each  spectral  ray  passing  through  a  lens 
has  its  own  principal  focus.  In  other  words,  the 
images  for  the  several  spectral  colors  do  not  coin- 
cide precisely.  The  order  in  which  the  refracted 
spectral  rays  cross  the  principal  axis  is  that  of 


INTRODUCTION   TO   PHYSIOLOGICAL    OPTICS      433 

their  refrangibility ;  violet  crosses  nearest  the 
lens,  then  blue,  green,  yellow,  orange,  and  red  in 
the  order  named.  The  principal  focus  will  thus 
be  a  line  of  colors  lying  in  the  principal  axis,  the 
end  nearest  the  lens  being  violet.  The  peripheral 
portions  of  a  lens  refract  rays  parallel  to  the  prin- 
cipal axis  more  strongly  than  the  axial  portion. 
Hence  the  chromatic  aberration  will  increase 
with  the  aperture  of  the  lens. 

Put  the  ground  glass  plate  and  the  diaphragm 
with  2  mm.  aperture  in  front  of  the  condenser. 
Let  the  rays  from  the  illuminated  spot  of  ground 
glass  pass  through  the  10  D  lens  placed  about 
15  cm.  in  front  of  the  ground  glass,  i.  e.  a  dis- 
tance somewhat  greater  than  the  focal  distance 
of  the  lens  (10  cm.).  Place  a  white  screen  about 
15  cm.  in  front  of  the  lens. 

The  image  of  the  white  spot  upon  the  ground 
glass  will  be  a  disk  with  violet  centre  and  red 
margin. 

Eemove  the  white  screen  farther  from  the  lens. 

At  a  distance  of  about  30  cm.  the  centre  of  the 
image  will  be  red  and  the  border  violet. 

The  image  in  this  experiment  is  blurred  be- 
cause the  rays  which  pass  through  the  peripheral 
portion  of  the  lens  cross  the  principal  axis  sooner 
than  the  rays  which  pass  through  the  axial  por- 
tion.    If  the  screen  be  placed  at  the  focus  of  the 

28 


434  THE    OUTGO    OF   ENERGY 

more  axial  rays,  this  focal  point  in  the  image  will 
be  surrounded,  by  dispersion  circles  made  by  the 
rays  which  have  been  refracted  from  the  periph- 
ery through  foci  nearer  the  lens  and  which  are 
now  diverging  from  these  foci.  If  the  screen  be 
placed  at  the  principal  focus  for  the  peripheral 
rays,  this  focal  point  will  be  surrounded  by  dis- 
persion circles  made  by  the  rays  that  have  not 
yet  converged  to  the  principal  axis.  (Compare 
spherical  aberration,  page  428.) 

Aberration  avoided  by  a  Diaphragm.  —  Place 
before  the  condenser  the  paper  diaphragm  with 
1  cm.  aperture. 

The  image  at  once  becomes  distinct,  and  the 
colors  practically  disappear.  The  outer  rays, 
which  when  refracted  would  cross  the  principal 
axis  far  enough  from  the  principal  focus  to  cause 
dispersion  circles,  have  been  cut  off'.  When  the 
aperture  of  a  lens  or  mirror  is  reduced  by  a 
diaphragm  to  10°,  the  greater  part  of  the  spheri- 
cal aberration  is  prevented. 

Spherical  aberration  is  still  further  reduced  by 
combining  several  lenses  in  an  objective  (apla- 
natic  system). 

With  an  achromatic  lens,  consisting  of  a  col- 
lecting lens  of  crown  glass  united  with  a  dispers- 
ing lens  of  flint  glass,  all  the  spectral  rays  may 
be  brought  to  the  same  focus,  and  chromatic 
aberration  altogether  avoided. 


INTRODUCTION    TO    PHYSIOLOGICAL    OPTICS 


Numbering  of  Prisms  and  Lenses 

Numbering  of  Prisms.  —  Prisms  may  be  num- 
bered according  to  refracting  angles  or  according 
to  the  extent  to  which  they  turn  the  light  ray 
from  its  course  (angular  deviation).  Angular 
deviation  is  expressed  by  the  methods  of  Dennett 
and  of  Prentice. 

Dennett's  method.  —  The  length  of  an  arc  of 
57.295°  equals  its  radius  of  curvature.  A  prism 
which  will  bend  the  ray  one  hundredth  part  of 
this  arc  is  called  one  centrad.  The  angular 
deviation  produced  by  the  prisms  are  by  this 
method  expressed  in  hundredths  of  the  radius 
measured  on  the  arc. 

Prentice's  method.  —  The  unit  of  comparison  is 
a  prism-dioptre,  i.  e.  a  prism  that  deflects  a  ray 
of  light  one  centimetre  at  a  plane  one  metre  dis- 
tant, or,  in  other  words,  the  hundredth  part  of 
the  radius  measured  on  the  tangent. 

Numbering  of  Lenses.  —  Lenses  are  numbered 
according  to  their  refractive  power.  The  unit  is 
a  lens  with  a  focal  distance  of  one  metre.  This 
unit  is  termed  a  dioptre,  D.  A  lens  of  two 
metres  focus  is  one  half  the  refractive  power,  or 
J  D.  The  lenses  ordinarily  employed  in  ophthal- 
mic practice  extend  from  0.12  D  to  22  D.     The 


436  THE   OUTGO   OF    ENERGY 

principal  focal  distance  of  any  lens  in  the  dioptric 
system  may  be  found  by  dividing  one  metre,  or 
100  cm.,  by  the  number  of  dioptres ;  thus  the 
focal  distance  of  a  lens  of  4  I)  =  •1|^-  =  25  cm. 

Convex  lenses  are  marked  -f,  concave  lenses  -. 

If  two  or  more  lenses  are  placed  together,  the 
dioptric  power  of  the  system  thus  formed  equals 
the  algebraical  sum  of  the  dioptric  powers  of 
the  lenses  in  the  system. 


REFRACTION   IN    THE    EYE  437 


IX 
REFRACTION  IN   THE  EYE 

The  Eye  as  a  Camera  Obscura.  —  1.  From  the 
eye  of  an  ox  remove  the  posterior  part  of  the 
sclerotic  and  choroid  coats  over  an  area  about 
1  cm.  in  diameter  near  the  outer  (temporal)  side 
of  the  optic  nerve.  Cover  the  retina  with  a  watch 
glass.  Turn  the  cornea  towards  an  incandescent 
lamp. 

A  small,  real,  inverted  image  of  the  lamp 
will  be  seen  upon  the  transparent  retina.  In  the 
white  rabbit  the  choroid  has  so  little  pigment  that 
the  retinal  image  may  be  seen  without  removing 
the  outer  coats  of  the  eye. 

2.  In  a  darkened  room,  direct  a  blond,  blue- 
eyed  individual  to  turn  the  eyes  so  that  one 
cornea  shall  lie  in  the  outer  angle  of  the  eye. 
Hold  a  candle  near  the  temporal  side  of  that 
eye. 

The  small,  inverted  retinal  image  of  the 
candle  can  often  be  seen  shining  through  the 
sclerotic  coat  at  the  nasal  side  of  the  eye. 


438  THE    OUTGO   OF   ENERGY 


The  Schematic  Eye 

In  passing  from  the  external  air  to  the  retina, 
the  rays  of  light  undergo  refraction  at  the  layer 
of  tears  on  the  anterior  surface  of  the  cornea,  the 
surfaces  bounding  layers  of  unequal  refractive 
power  in  the  substance  of  the  cornea,  the  ante- 
rior surface  of  the  aqueous  humor,  the  anterior 
surface  of  the  lens,  the  surfaces  bounding  layers 
of  unequal  refractive  power  in  the  substance  of 
the  lens,  and  the  anterior  surface  of  the  vitreous 
humor.  To  determine  the  size  and  position  of 
visual  images,  it  is  fortunately  not  necessary  to 
calculate  refraction  at  each  of  these  many  sur- 
faces. The  problem  is  much  simplified  by  the 
following  considerations. 

The  irregularities  in  the  refractive  power  of 
the  different  parts  of  the  cornea  are  small ;  and 
the  refractive  index  of  the  layer  of  tears  which 
covers  the  anterior  surface  is  almost  identical 
with  the  index  of  the  substance  of  the  cornea 
and  that  of  the  aqueous  humor.  Practically 
therefore  the  layer  of  tears,  the  cornea,  and  the 
aqueous  humor  may  be  regarded  as  a  single  re- 
fracting medium.  Further,  although  the  layers 
of  which  the  lens  is  composed  increase  in  refract- 
ing power  towards  the  centre  of  the  lens,  it  is 


KEFR ACTION  IN  THE  EYE        439 

known  that  the  error  introduced  by  assuming 
the  lens  to  be  homogeneous  is  unimportant. 
Thus  the  simplified  dioptric  system  of  the  eye 
consists  of  three  refracting  surfaces  :  the  anterior 
surface  of  the  cornea,1  the  anterior  surface  of  the 
lens,  and  the  anterior  surface  of  the  vitreous 
humor.  The  index  of  refraction  of  the  aqueous 
and  vitreous  humors  is  practically  the  same. 

The  several  refracting  surfaces  of  this  optical 
system  are  approximately  "  centred,"  i.  e.  placed 
with  their  centres  of  curvature  upon  a  right  line, 
the  optical  axis.  The  diaphragm  (iris)  is  of  such 
a  size  and  position  that  the  rays  entering  the  eye 
intersect  the  axis  at  small  angles  ;  the  aperture 
of  the  system  is  therefore  small.  Under  such 
conditions  it  is  possible  to  find  upon  the  princi- 
pal axis  of  the  system  certain  cardinal  points, 
discovered  by  Gauss,  by  the  aid  of  which  the 
situation  and  size  of  the  visual  images  may  be 
determined.  The  cardinal  points  are  (1)  the  an- 
terior principal  focus,  (2)  the  anterior  principal 
point,  (3)  the  posterior  principal  point,  (4)  the 
anterior  nodal  point,  (5)  the  posterior  nodal  point, 
(6)  the  posterior  principal  focus.  These  points 
are  reciprocal. 

As  the  dioptric  system  of  the  eye  consists  of  a 

1  For  convenience,  the  anterior  surface  of  the  cornea  will  be 
held  to  include  the  layer  of  tears. 


440  THE    OUTGO    OF   ENERGY 

spherical  surface 1  (the  cornea)  and  a  double  con- 
vex lens  (the  crystalline  lens)  it  will  be  advis- 
able to  consider  first  the  cardinal  points  of  the 
cornea  (System  A),  next  those  of  the  lens  (Sys- 
tem B),  and  finally  those  of  the  two  combined 
as  in  the  eye  (System  C). 

Cardinal  Points  of  the  Cornea  (System  A) 

Construction  Drawing  of  System  A.  —  Draw 
a  horizontal  line  to  serve  as  the  optical  axis.2 
Take  any  point,  k,  in  this  line  for  a  centre  of 
curvature.3      From    this    point    describe   an    arc 

1  The  cornea  is  not  strictly  a  spherical  surface,  but  more 
nearly  that  produced  by  the  revolution  of  an  ellipse  about  its 
major  axis. 

2  This  construction  drawing  should  be  placed  near  the  top  of 
the  page,  in  order  to  permit  the  construction  drawings  for  the 
lens  and  the  compound  optical  system  to  be  made  beneath  it. 
All  these  drawings  will  be  the  natural  size. 

8  The  following  list  will  be  found  convenient  : 
k,  centre  of  curvature. 
r,  radius  of  curvature. 
hlt  intersection  of  the  first  spherical  surface  of  any  system  with 
its  principal  axis  ("  first  "  is  used  in  the  sense  of  nearest 
the  source  of  light). 
h2,  intersection  of  the  second  spherical  surface  with  its  principal 

axis. 
nlt  the  first  medium,  that  which  bounds  the  refracting  surface 
on  the  side  from  which  the  ray  conies  ;  also  the  refractive 
index  of  this  medium. 
u2,  The  second  medium,  that  which  bounds  the  refracting  sur- 
face on  the  side  from  which  the  ray  emerges  ;  also  the 
refractive  index  of  this  medium. 


REFRACTION   IN    THE    EYE  441 

with  the  radius  r  =  7.829  mm.,  the  radius  of 
curvature  of  the  cornea.  The  intersection  of 
the  arc  with  the  axis  is  termed  the  principal 
point  hx  of  the  axial  ray.  The  spherical  surface 
separates  two  media :  nv  the  air,  and  n2,  the 
aqueous  humor. 

Principal  Focal  Distances.  —  1.  Kays  passing 
from  the  first  medium  through  the  cornea  into 
the  second  medium  unite  nearly  in  a  point,  the 
posterior  principal  focus,  <£2.  The  distance,  h^*, 
between  this  point  and  the  principal  point  is  the 
posterior  principal  focal  distance,  F2.  Eays  pass- 
ing from  the  aqueous  humor  through  the  cornea 

<pi,  anterior  principal  focus. 

02>  posterior  principal  focus. 

Fx,  anterior  focal  distance. 

F2,  posterior  focal  distance. 

fl,  anterior  conjugate  focal  distance. 

f2,  posterior  conjugate  focal  distance. 

o,  optical  centre. 
Klt  first  nodal  point. 
K2,  second  nodal  point. 
Hi,  first  principal  point. 
H2,  second  principal  point. 

5,  point  between  two  refracting  surfaces  at  which  an  object 
must  be  in  order  that  the  images  of  the  object  formed  by 
the  refracting  surfaces  shall  be  similar,  i.  e.,  images  of 
one  another,  lying  therefore  in  the  principal  surfaces. 

Where  confusion  might  arise  in  applying  these  terms  to  Sys- 
tem A,  B,  orC,  they  will  be  distinguished  by  placing  with  them 
the  letters  A,  B,  C,  respectively.  Thus  the  anterior  focal  dis- 
tance of  the  lens  will  be  written  Fi  B,  wherever  it  might  other* 
wise  be  confused  with  that  of  System  A  or  C. 


442  THE    OUTGO    OF   ENERGY 

to  the  air,  parallel  to  and  near  the  axis,  unite  in 
front  of  the  cornea  nearly  in  a  point,  the  anterior 
principal  focus,  <£i.  The  distance,  ht  </>b  between 
this  point  and  the  principal  point  is  the  anterior 
principal  focal  distance,  Fx.  The  principal  focal 
distances  are  proportional  to  the  coefficients  of 
refraction  of  the  first  and  last  media.  The  pos- 
terior principal  focal  distance  is  calculated  by 
the  formula  * 

(la.)  F2=     "*r 


no  —  n. 


In  comparing  refractive  powers  the  air,  nlt  is 
taken  as  the  unit.     Thus  the  formula  becomes 


(1  b)  F2 


n2  r 


n2  —  1 


The  anterior  principal  focal  distance  is  calcu- 
lated by  tne  formula 

(2  a)  FX=     *' 


no  —  n. 


As  %i  =  unity,  the  formula  becomes 

(2  b)  Ft  =  —^-r 

n2  —  1 
The  refractive  index,  nu  of  the  air  =  1 ;  accord- 

1  For  the  derivation  of  the  formulas  in  this  chapter  the 
reader  is  referred  to  the  works  of  Donders  (Accommodation  and 
Refraction  of  the  Eye)  and  Helmholtz  (Handhuch  der  physio- 
logischen  Optik). 


REFRACTION   IN   THE   EYE  443 

ing  to  Helmholtz,1  the  refractive  index,  n2,  of  the 
aqueous  humor  is  1.3365  ;  the  ratio  is  f. 

Calculate  F1  and  F,.  The  result  is,^i  =  23.266, 
F2  =  31.095. 

2.  The  principal  foci  may  also  be  approximately 
found  by  construction.  Erect  at  the  principal 
point  and  the  nodal  point 2  perpendiculars  to  the 
optical  axis.  Set  off  on  each  perpendicular  dis- 
tances from  the  optical  axis  proportional  to  the 
rapidity  of  light  in  the  first  and  second  medium. 
The  ratio  in  the  case  of  the  air  and  the  aqueous 
humor  is  4  '.  3.  Mark  therefore  points  20  mm. 
and  15  mm.  from  the  axis.  Draw  a  line  from  the 
20  mm.  point  of  the  first  perpendicular  through 
the  15  mm.  point  of  the  second,  and  produce  the 
line  to  the  optical  axis.  Its  intersection  with 
the  optical  axis  is  the  posterior  principal  focus. 
Find  in  a  similar  way  the  anterior  principal 
focus.  Indicate  upon  the  axis  the  cardinal  points, 
remembering  that  the  construction  drawing  is  to 
be  the  natural  size. 

Construction  of  Image.  —  About  10  cm.  in 
front  of  the  cornea  draw  an  arrow,  ij,  which 
shall  intersect   the   optical  axis  at  right  angles. 

1  The  figures  for  this  and  subsequent  calculations  under  "  Re- 
fraction of  the  Eye,"  are  those  given  by  Helmholtz.  They  are 
collected  in  a  convenient  Table  on  pages  461  and  462. 

2  The  centre  of  curvature  is  the  nodal  point  of  a  system  con- 
sisting of  a  single  spherical  surface. 


444  THE    OUTGO    OF    ENERGY 

Draw  a  line  from  the  point  i  of  the  arrow 
through  k.  This  line,  since  it  passes  through 
the  centre  of  curvature,  will  coincide  with  the 
perpendicular  to  the  refracting  surface,  and  there- 
fore will  not  be  refracted.  Draw  from  the  point 
i  to  the  cornea  a  line  parallel  to  the  axis.  This 
parallel  ray  will  be  refracted  through  the  poste- 
rior principal  focus  <f>2.  The  two  rays  will  unite 
at  their  point  of  intersection,  i2,  which  point  is 
the  image  of  i  and  is  its  conjugate  focus.  The 
arrow  ij  was  vertical  to  the  axis.  Hence  its 
image  will  also  be  vertical  to  the  axis.  Draw, 
therefore,  from  i2  a  line  vertical  to  the  axis. 
From  the  end  j  of  the  arrow  draw  a  line  through 
k.  The  intersection  of  this  line  witli  the  verti- 
cal line  just  drawn  will  be  the  image  j2  of  the 
point  j. 

Calculation  of  the  Position  of  the  Conjugate 
Foci.  —  The  conjugate  foci  may  be  found  by  the 
following  formulas.  Let  /i  be  the  conjugate 
focal  distance  hi  i,  and  f2  be  the  conjugate  focal 
distance  h\jr 

\o  a)     fx  =  - —  (4  a)     f2  - 


A- Ft  v      J     "*     fi-Fi 

For  virtual  images  the  formulas  become 

(3b)    /.  =  ^4         <4b)    fi^TT** 


REFRACTION    IN    THE    EYE  445 


Cardinal  Points  of  the  Crystalline  Lens 
(System  B) 

Construction  Drawing  of  System  B.  —  When 
the  lens  is  accommodated  for  distant  vision  the 
radius  of  the  anterior  surface  is  about  10  mm., 
the  radius  of  the  posterior  surface  about  6  mm. ; 
the  thickness  at  the  principal  axis  3.6  mm.  The 
index  of  refraction  of  the  lens  is  1.4371.  The  in- 
dex of  the  aqueous  and  vitreous  humors  is  1.3365. 

Beneath  the  construction  drawing  of  the 
cardinal  points  of  the  cornea  (System  A)  draw 
a  horizontal  line  parallel  to  the  optical  axis 
of  the  cornea.  This  line  will  serve  as  the 
optical  axis  of  the  lens.  From  the  intersection 
of  the  cornea  with  its  optical  axis  let  fall  a 
perpendicular  to    the    optical   axis  of   the   lens. 

The  anterior  surface  of  the  lens  intersects  the 
optical  axis  3.6  mm.  posterior  to  the  cornea. 
The  radius  of  the  anterior  surface  of  the  lens  is 
10  mm.  Find  therefore  on  the  optical  axis  a 
point  3.6  +  10  =  13.6  mm.  behind  the  cornea. 
From  this  point  as  a  centre  describe  an  arc  with 
a  radius  of  10  mm.  that  shall  intersect  the  optical 
axis  3.6  mm.  behind  the  cornea.  A  segment  of 
this  arc  will  represent  the  anterior  surface  of 
the  lens. 


446  THE    OUTGO    OF    ENERGY 

The  thickness  of  the  lens,  accommodated  for 
distant  objects,  is  3.6  mm.  Mark  this  point. 
Here  the  posterior  surface  of  the  lens  intersects 
the  optical  axis.  The  radius  of  the  posterior  sur- 
face is  6  mm.  Find  therefore  a  point  on  the 
optical  axis  6  mm.  in  front  of  the  posterior  sur- 
face of  the  lens.  With  this  point  as  a  centre 
describe  with  a  radius  of  0  mm.  the  segment  of 
the  arc  that  shall  represent  the  posterior  surface 
of  the  lens.  Mark  upon  this  drawing  the  cardi- 
nal points  of  the  lens,  as  follows. 

Optical  Centre.  —  In  the  cornea,  a  simple  spher- 
ical surface,  rays  directed  to  the  centre  of  curva- 
ture, k,  were  found  to  pass  through  the  refracting 
surface  unchanged  in  direction.  In  thin  convex 
lenses  having  a  long  focal  distance  it  is  generally 
assumed  that  any  ray  passing  through  a  point 
within  the  lens  termed  the  optical  centre,  o,  is  not 
refracted.  In  thick  lenses,  on  the  contrary,  every 
ray  excepting  that  coinciding  with  the  principal 
axis  is  refracted  (see  Nodal  Points). 

The  optical  centre  is  situated  in  the  prin- 
cipal axis  within  the  lens.  In  a  lens  bounded  on 
both  sides  by  media  of  equal  refracting  power, 
for  example,  the  crystalline  lens  bounded  by  the 
aqueous  and  vitreous  humors,  the  optical  centre 
is  found  by  dividing  the  axis  of  the  lens,  i.  e.} 
the  distance  between  the  refracting  surfaces  on 


REFRACTION   IN   THE    EYE  447 

the  principal  axis,  into  two  parts  proportionate 
to  the  radii  of  the  refracting  surfaces. 
Then 

10  +  6  :  3.6  =  6  :  x 

x—  1.35    mm.,  the  distance  of  o  from  the  pos- 
terior refracting  surface. 
Then 

3.6  -  1.35  =  2.25  mm., 

the    distance    of  o  from  the  anterior  refracting 
surface. 

Nodal  Points.  —  In  thick  lenses  (such  as  the 
crystalline)  with  short  focal  distance,  all  the  rays 
except  that  which  coincides  with  the  principal 
axis  are  refracted  at  one  or  both  of  the  spherical 
surfaces.  In  order  to  determine  the  path  of  rays 
passing  through  the  lens  it  is  necessary  to  find 
the  nodal  points.  These  are  two  points  so  placed 
that  a  ray  directed  to  the  first  point  appears  on 
leaving  the  lens  to  have  come  from  the  second 
point,  in  a  direction  parallel  to  the  entering  ray. 
All  rays  coming  from  the  optical  centre,  o,  to  the 
anterior  refracting  surface  will  after  refraction 
appear  to  have  come  from  the  first  nodal  point, 
Kx,  situated  within  the  lens  on  the  principal  axis, 
between  o  and  h*.  Similarly,  all  rays  from  o  to 
the  posterior  refracting  surface  will  appear  to 
have  come  from  the  second  nodal  point,  K%,  situ- 


448  THE    OUTGO   OF   ENERGY 

a  ted  between  o  and  h2.  Thus  o  and  Kx  are  con- 
jugate foci  for  the  surface  hi,  and  o  and  K2  are 
conjugate  foci  for  the  surface  h2.  K\  and  K2 
are  virtual  images  of  o;  that  is,  if  o  were  observed 
through  the  surface  hx  the  image  would  appear 
to  be  A'i,  while  if  o  were  observed  through  hz 
the  image  would  appear  to  be  K2.  As  the  nodal 
points  are  images  of  the  same  point  o,  they  must 
therefore  be  images  of  each  other. 

The  first  nodal  point,  Ku  which  is  the  virtual 
image  of  the  optical  centre,  o,  formed  by  rays 
passing  from  o  through  the  anterior  refracting 
surface,  hu  and  which  lies  at  the  conjugate  focus 
of  o,  is  situated  2.126  mm.  behind  the  anterior 
surface  of  the  lens  (accommodated  for  distant 
objects).  The  second  nodal  point,  K2,  the  virtual 
image  of  o  formed  by  rays  passing  from  o  through 
the  posterior  refracting  surface,  h2,  is  situated 
1.276  mm.  in  front  of  the  posterior  surface  of  the 
lens  (accommodated  for  distant  objects).  The  dis- 
tance between  the  two  nodal  points  is  0.198  mm. 

Principal  Surfaces.  —  Within  a  double  convex 
lens  are  two  parallel  planes,  termed  the  principal 
surfaces.  They  are  perpendicular  to  the  prin- 
cipal axis  and  are  so  placed  that  the  emerging 
ray  appears  to  come  from  a  point  in  the  second 
principal  surface  that  exactly  corresponds  to  the 
point  in  the  first  principal  surface  to  which  the 


REFRACTION    IN    THE    EYE  449 

entering  ray  is  directed.  Thus  the  point  in 
the  second  principal  surface  from  which  the 
emergent  ray  appears  to  come  is  the  same  dis- 
tance from  the  axis  as  the  corresponding  point 
in  the  first  principal  surface  to  which  the  enter- 
ing ray  appears  to  pass.  In  short,  each  principal 
surface  is  the  image  of  the  other,  and  is  of  equal 
size. 

To  determine  the  position  of  the  principal  sur- 
faces there  must  be  found  between  the  two 
refracting  surfaces  a  point,  s,  at  which  an  object 
will  form  similar  images  with  each  refracting 
surface.  These  images  being  similar  are  images 
of  each  other  and  of  equal  size.  The  planes  in 
which  they  lie  are  the  principal  surfaces. 

The  Point  s.  —  The  point  s  lies  between  the 
two  refracting  surfaces  at  distances  proportional 
to  the  principal  focal  distance  of  each.  It  will 
be  remembered  that  the  point  o  was  found  by 
dividing  the  distance  between  the  two  refracting 
surfaces  into  two  parts,  proportional  to  the  radii 
of  curvature  of  the  two  surfaces.  In  System  B 
the  two  refracting  surfaces  are  the  anterior  and 
posterior  surfaces  of  the  crystalline  lens,  which 
is  bounded  by  the  aqueous  and  vitreous  humors, 
media  of  equal  refractive  power.  The  focal  dis- 
tances of  the  refracting  surfaces  are  in  this  case 

proportional  to  the  radii  of  curvature.     Thus  the 

29 


450  THE    OUTGO   OF   ENERGY 

division  of  the  distance  between  the  refracting 
surfaces  is  the  same  for  both  s  and  o,  and  there- 
fore s  and  o  coincide.  In  System  C,  on  the  con- 
trary, the  first  medium  is  the  air,  and  the  last 
the  vitreous  humor.  The  principal  focal  dis- 
tances are  proportional  to  the  coefficients  of  re- 
fraction of  the  first  and  last  media ;  they  are 
no  longer  proportional  to  the  radii  of  curvature ; 
therefore  s  and  o  no  longer  coincide,  and  their 
images,  lying  in  the  principal  surfaces  and  at 
the  nodal  points,  respectively,  no  longer  coincide, 
but  must  be  found  separately. 

Principal  Points.  —  At  the  intersection  of  the 
principal  surfaces  with  the  principal  axis  lie  the 
principal  points,1  Hx  and  ff2.  The  second  princi- 
pal point  is  the  image  of  the  first.  Kays  which 
in  the  first  medium  are  directed  to  the  first 
principal  point  are  directed  to  the  second  princi- 
pal point  in  the  last  medium,  i.  e.,  after  the  last 
refraction.  The  anterior  principal  focal  distance 
is  calculated  from  the  first  principal  point,  and 
the  posterior  principal  focal  distance  from  the 
second  principal  point 

Principal  Focal  Distances.  —  The  posterior  focal 
distance  of   the  lens  (accommodated  for  distant 

1  The  principal  points,  Hx  and  7f2,  coincide  with  the  nodal 
points,  A\  and  K2,  when  the  first  and  last  media  of  the  optical 
system  have  the  same  refractive  power. 


KEFRACTION    IN    THE    EYE  451 

objects)  is  50.617  mm.  The  anterior  focal  dis- 
tance is  the  same,  for  the  lens  is  bounded  by 
media  of  equal  density. 


Cardinal  Points  of  the  Eye  (System  C) 

Examine  construction  drawings  of  System  A 
(the  cornea)  and  System  B  (the  lens).  System  C 
must  be  a  combination  of  A  and  B. 

Note  :  1.  With  System  C  as  with  System  A 
the  first  and  last  media  have  different  refractive 
powers.  Therefore  the  principal  points  cannot 
coincide  with  the  nodal  points.  2.  The  relation 
between  the  nodal  point  k  of  System  A  and 
the  nodal  points  K\  and  K2  of  System  B  is  such 
that  the  nodal  points  of  System  C  will  lie  near 
the  posterior  surface  of  the  crystalline  leus. 
3.  The  principal  point  hi  of  System  A  lies  on 
the  anterior  surface  of  the  cornea,  and  the  prin- 
cipal points  H\  and  H2  of  System  B  lie  in  the 
lens.  Hence  those  of  System  C  must  lie  in  the 
aqueous  humor.  4.  In  System  C  the  collecting 
power  of  System  B  is  added  to  that  of  System 
A.  The  focal  distances  in  System  C  will  there- 
fore be  less  than  those  of  A  or  B. 

Principal  Surfaces.  —  The  principal  surfaces  are 
found  from  the  point  s.  If  a  perpendicular  be 
drawn  at  s  the  image  of  that  perpendicular  formed 


452  THE    OUTGO    OF   ENERGY 

by  the  cornea  will  be  of  equal  size  with  the  image 
of  it  formed  by  the  crystalline  lens.  These  simi- 
lar images  will  lie  in  the  principal  surfaces.  The 
image  which  the  cornea  forms  of  the  point  s  will 
be  the  first  principal  point,  Hx  of  System  C,  and 
the  image  which  the  lens  forms  of  s  will  be  the 
second  principal  point,  H2  of  System  C.  The 
point  s  lies  between  hi  of  System  A  and  H1  of 
System  B,  at  distances  proportional  to  the  pos- 
terior focal  distance  (i^  =  31.095  mm.),  of  System 
A  and  the  anterior  focal  distance  (Fx  =  50.617 
mm.)  of  System  B.  The  distance  between  hi,  which 
lies  at  the  anterior  surface  of  the  cornea,  and 
HXB,  which  lies  2.126  mm.  behind  the  anterior 
surface  of  the  lens,  is  3.6  mm.  (the  distance  be- 
tween the  cornea  and  the  lens)  plus  2.126  mm. 
=  5.726  mm.  This  distance  is  to  be  divided  in 
the  proportion  50.617  :  31.095. 

50.617  +  31.095  :  31.095  ::  5.726  :  x. 

x—  2.179.  Hence  s  lies  2.179  mm.  behind  the 
cornea,  and  5.726  —  2.179  =  3.547  mm.  in  front  of 
the  anterior  principal  point  of  the  crystalline  lens. 
The  first  or  anterior  principal  point  of  the  eye, 
H\G,  is  the  virtual  image  of  s  formed  by  the 
cornea  ;  it  lies  at  the  conjugate  focus  of  s,  and 
its  position  is  determined  by  the  formula  (3  b), 
page  444. 


REFRACTION   IN   THE   EYE  453 

Fx  A  =  23.266  mm. 

F2  A  =  31.095  mm. 

f2A*  =    2.179  mm, 

The  first  principal  point,  Hx  C,  is 

23.266  x  2.179        1  _.  ,    ,.    ,    ,     ., 

=  1.75    mm.   behind   hi   the  an- 

31.095  -  2.179 

terior  surface  of  the  cornea. 

The  second  or  posterior  principal  point  of  the 

eye,  H2  C,  is  the  virtual  image  of  s  formed  by  the 

lens.     It  also  is  found  by  formula  (3  b). 

F1  B  =  50.617  mm. 

F2  B  =  50.617  mm. 

f2£^  =    3.547  mm. 

The  second  principal  point,  H2  C,  is 

50.617  x  3.547      0  oi ,  ,    .        ., 

xfrwTTj q  ca7  =  3.814  mm.  before  the  posterior 

principal  point  of  the  lens ;  this  point  lies  5.924 
mm.  behind  the  cornea ;  hence  H2  C  lies  5.924 
—  3.814  =  2.11  mm.  behind  the  anterior  surface 
of  the  cornea.  The  distance  between  the  two 
principal  points  is  2.11  —  1.75  =  0.36  mm. 

Nodal  Points.  —  The  nodal  points  are  virtual 
images  of  the  point  o,  which  divides  the  distance 
between  the  nodal  points  of  System  A  and  Sys- 

*  The  distance  of  the  object  s  from  the  refracting  surface, 
in  this  case,  the  cornea. 

t  The  distance  of  the  object  s  from  the  anterior  principal 
point  of  the  crystalline  lens. 


454  THE    OUTGO    OF   ENERGY 

tera  B  iuto  two  parts,  proportional  to  the  anterior 
focal  distance  of  the  cornea  (23.266  mm.)  and  the 
focal  distance  of  the  lens  (50.617  mm.).  As  K1  A 
lies  7.829  mm.  and  Kx  B  5.726  mm.  behind  the  cor- 
nea, the  distance  between  them  is  2.103  mm.  This 
is  to  be  divided  in  the  proportion  23.266  :  50.617. 
23.266+  50.617:  50.617::  2.103  :  x.  £  =  1.4408. 
Thus  o  lies  1.4408  mm.  behind  the  first  principal 
point  of  the  crystalline  lens  (S}7stem  B)  and 
consequently 

5.726  +  1.4408  =  7.167  mm. 

behind  the  cornea. 

By  formula  (3  b),  A^i  C,  the  first  nodal  point  or 

the  image  of  o  formed  by  the  cornea,  is  found  to  be 

23.266  x  7.167      „  nr7  ,   - .    ,  ,, 

01  ~n^ —   _  .,  ._  =  6.9  /  mm.  behind  the  cornea. 

oLU9o  —  7.1b7 

The  second  nodal  point,  K2  C,  or  image  formed 

.     .     ^  „.       .  50.617  X  1.4408 

or  o  by  the   crystalline  lens,  is   rn  n17  _  -.  ^<ao 

=  1.401  mm.  behind  the  second  principal  point 
of  the  crystalline  lens,  and  consequently  5.924 
+  1.401  =  7.33  mm.  behind  the  cornea. 

The  distance  K\  K2  between  the  first  and 
second  nodal  points  of  System  C  is  7.33  — 
6.97  =  0.36  mm.     The  distance  Hi  H2  =  Kx  K2. 

Principal  Foci.  —  Kays  falling  on  the  cornea  par- 
allel to  the  principal  axis  are  refracted  by  hi  A  and 


BEFBACTION   IX   THE   EYE  455 

converged  to  the  point  <f>2A,  situated  31.095  mm. 
behind  the  cornea.  On  their  way  they  are  further 
refracted  by  System  B.  Hi  B  is  5.726  mm.  behind 
the  cornea.  The  point  <j>.2  A  is  31.095  —  5.726 
=  25.869  mm.  behind  Hx.  Calculated  from  H2  B, 
the  posterior  principal  focal  distance  F2  of  System 
B  is  50.617  mm.  The  posterior  focal  distance  of 
System  C  is  calculated  by  the  formula 

-  fiF2  25.369  x  50.617 

/2  =&  +  *[  A  =  25.369  +  50.617  =  168"  mm« 

behind  Hz  B,  and  hence  16.899  +  5.924  = 
22.823  mm.  behind  the  cornea,  and  22.823  — 
2.11  =  20.713  mm.  behind  H,  of  System  C. 
The  posterior  principal  focal  distance  of  the  eye 
is  therefore  20.71  mm. 

Parallel  rays  falling  on  the  posterior  surface  of 
the  lens  are  refracted  by  the  lens  and  converge 
at  a  point  (f)1  B  —  50.617  mm.  in  front  of  Hi  B. 
They  meet  the  anterior  surface  of  the  cornea 
50.617  -  5.726  =  44.891  mm.  from  H1  B.  They 
are  further  converged  by  the  cornea  to 

23.266  x  44.891       .0fTK 
31.095  +  44.891  =  13-'omm- 

before  the  cornea,  or  13.75  +  1.75  =  15.5  mm. 
before  Hr  C.  The  anterior  principal  focal  dis- 
tance of  the  eye  is  therefore  15.5  mm.1 

1  In  this  discussion  I  have  followed  closely,  in  some  places 


456  THE    OUTGO    OF   ENERGY 


Calculation  of  the  Situation  and  Size  of 
Dioptric  Images 

Draw  perpendiculars  through  the  optical  axis 
of  System  C  at  the  following  points  :  the  anterior 
principal  focus,  </>i  0,  the  first  principal  point, 
Hi  C,  the  second  principal  point,  H2  C,  and  the 
posterior  principal  focus,  <£2  0  (retina).  Mark  on 
the  optical  axis  the  first  and  second  nodal  points, 
Kx  C  and  K2  C. 

The  following  facts  should  he  borne  in  mind : 

1.  Every  ray  which  in  the  first  medium  is 
directed  to  the  first  nodal  point  appears  in  the 
last  medium  to  come  from  the  second  nodal 
point   and   is   parallel    to   its  original  direction. 

2.  The  point  at  which  the  ray  cuts  the  second 
principal  surface  is  the  same  distance  from  the 
optical  axis  as  the  point  at  which  the  ray  cuts 
the  first  principal  surface ;  between  the  prin- 
cipal surfaces  the  ray  is  parallel  to  the  optical 
axis.  3.  All  rays  parallel  in  the  first  medium 
unite  in  one  point  in  the  second  or  posterior  focal 
surface  (the  plane  passing  through  the  posterior 
principal  focus  vertical  to  the  optical  axis)  ;   if 

almost  literally,  the  valuable  works  of  1  londers  ( A  ceo  vn  modal  inn 
ami  Refraction  of  tin;  Eye,  New  Sydenham  Society,  London, 
1864)  and  Helmholtz  (Handbuch  der  pliysiologischen  Optik, 
2te  Auflage,  1896), 


REFRACTION    IX    THE   EYE  457 

these  rays  be  parallel  to  the  axis  they  will  unite 
in  the  posterior  principal  focus.  Conversely,  all 
rays  parallel  in  the  second  medium  unite  in  one 
point  on  the  first  or  anterior  focal  surface,  and  if 
parallel  to  the  axis  they  unite  at  the  anterior 
principal  focus  (Gauss). 

1.  Find  the  course  in  the  vitreous  humor  of 
any  ray,  ab,  which  enters  the. eye. 

Draw  in  the  first  medium  a  ray,  a1  b',  parallel 
to  a  b,  directed  to  the  first  nodal  point.  In  the 
second  medium  draw  this  ray,  parallel  to  its  origi- 
nal direction,  from  the  second  nodal  point  to  the 
posterior  focal  surface.  Then  a  b  must  also  meet 
the  posterior  focal  surface  at  this  same  place ;  for 
all  rays  parallel  in  the  first  medium  converge  in 
the  second  medium  to  one  point  in  the  posterior 
focal  surface.  Produce  a  b  to  the  first  principal 
surface,  thence,  parallel  with  the  optical  axis,  to 
the  second  priucipal  surface,  thence,  through  the 
vitreous  humor,  to  the  point  already  found  in  the 
posterior  focal  surface. 

2.  Let  i  be  any  point  in  the  first  medium  (the 
air).  Find  its  image  (for  convenience  i  should 
be  placed  at  least  10  cm.  in  front  of  the  cornea). 

Draw  from  i  a  ray,  iij\,  through  the  first  and 
second  nodal  points,  as  directed  above.  Draw 
from  i  a  second  ray,  i2j2,  parallel  with  the  optical 
axis.     This  rav  will  cut  the  second  focal  surface 


458  THE    OUTGO    OF   ENERGY 

at  the  principal  focus.  Produce  i2j>2  until  it  meets 
tijfi.  The  point  of  intersection  will  be  the  image 
of  the  point  i. 

Eeduced  Eye 

The  distance  of  less  than  one  fourth  millimetre 
which  separates  one  principal  point  from  the 
other  is  so  small  that  it  may  be  neglected  with- 
out any  error  of  practical  importance.  Thus  the 
two  principal  points  may  be  combined  in  one  point 
lying  2.34  mm.  behind  the  anterior  surface  of  the 
cornea  of  the  normal.1  Similarly  the  two  nodal 
points  may  be  combined  in  one  point  lying 
0.48  mm.  in  front  of  the  posterior  surface  of  the 
lens,  or  about  16  mm.  in  front  of  the  retina. 
The  nodal  point  k  of  the  cornea  (System  A)  is 
about  14  mm.  in  front  of  the  retina.  The  nodal 
point  of  the  lens  and  that  of  the  cornea  are  com- 
bined in  the  reduced  eye  in  a  nodal  point  situated 
15  mm.  from  the  retina.  The  lens  may  therefore 
be  omitted.  Indeed,  the  cornea  is  normally  the 
principal  refracting  surface ;  its  focal  distance  is 
31.095  mm.,  while  that  of  the  crystalline  lens  is 
50.617  mm.  ;  if  the  lens  were  not  present,  parallel 
rays  entering  the  eye  would  be  focussed  by  the 

1  Listing:  Wagner's  Handworterbuch  der  Physiologie,  1853, 
iv.,  p.  495. 


HEfHACTION    IN    THE    EYE  459 

cornea  in  a  point  about  10  mm.  behind  the  retina. 
Thus  the  eye  is  reduced  to  a  single  refracting 
surface,  the  cornea,  separating  two  media,  the  air 
and  the  vitreous  humor.  The  index  of  refraction 
of  these  media  is  -|.  The  principal  focal  distances 
are  proportional  to  the  coefficients  of  refraction 
of  the  first  and  last  media ;  i<\  is  15  mm.  and  Fs 
20  mm.,  measured  from  the  principal  point.  The 
visual  axis  (from  the  cornea  to  the  retina  of  the 
reduced  eye)  is  therefore  20  mm.  In  order  to 
bring  parallel  rays  to  a  focus  at  20  mm.,  the 
index  of  refraction  being  J,  the  radius  of  curva- 
ture of  the  cornea  of  the  reduced  eye  should  be 
5  mm. 

In  such  a  reduced  eye  trie  retinal  images  have 
the  same  position  and  size  as  in  the  ordinary 
eye.  The  reduced  eye  is  shown  in  normal  size 
in  Fig.  65. 


Fig.  65.  The  reduced  eye.     Normal  size  (Bonders). 

K  is  the  optical  centre  or  nodal  point. 
h,  the  principal  point. 

K h  =  5  mm.,  the  radius  of  curvature  of  the 
refracting  surface. 


460  THE    OUTGO   OF   ENEKGY 

</>!,  the  anterior  principal  focus,  —  the  focus  of 
rays  parallel  in  the  vitreous. 

<fi2,  the  posterior  principal  focus,  —  the  focus 
of  rays  parallel  in  the  air. 

h  cf>1  =  2*1,  the  anterior  focal  distance,  =  15  mm. 

h  cf>2  =  F2t  the  posterior  focal  distance,  =  20  mm. 

n1~3~  Ft  7"  15' 

With  the  reduced  eye  many  calculations  may 
be  rapidly  and  easily  performed. 


REFRACTION    IN   THE    EYE 


461 


AVERAGE  MEASUREMENTS   OF  NORMAL 
(EMMETROPIC)   EYE1 


mm. 

12 

4 

1 

Thickness  of  lens  accommodated  for  near 

4 

Thickness  of  lens  accommodated  for  distant 

3.6 

0.2-0.3 

Distance  between  retinal  vessels 

5    and   rod 

0.2-0.3 

1.5 

1.25 

Diameter  of  fovea  centralis  .     = 

. 

0.22 

0.004-0.005 
0.0018 

Accommodated  for 

Distant 

Near 

objects. 

objects. 

Refractive   index   of  aqueous 

and  vitreous  humors    .     . 

1.3365 

1.3365 

Total  refractive  index  of  crys- 

1.4371 

1.4371 

Radius  of  curvature  of  cornea  . 

7.829 

7.829 

Radius  of  curvature  of  ante- 

rior surface  of  lens  .     .     . 

10.00 

6.0 

Radius  of  curvature  of  poste- 

rior surface  of  lens      .     . 

6.0 

5.5 

1  It  should  be  understood  that  the  figures  given  in  this  table 
are  the  mean  of  numerous  observations.  The  variation  in 
different  eyes  is  considerable,  though  in  most  cases  not  great 
enough  to  be  of  practical  importance. 


462 


THE    OUTGO    OF    ENERGY 


Accommodated  for 

Distant 

Near 

objects. 

objects. 

Distance  from  anterior  surface 

of  cornea  to  anterior  sur- 

face of  lens 

3.6 

3.2 

Distance  from  anterior  surface 

of  cornea  to  posterior  sur- 

face of  lens 

7.2 

7.2 

Calculated 

Anterior   principal   focal  dis- 

tance of  cornea  .... 

23.266 

23.266 

Posterior  principal  focal  dis- 

tance of  cornea  .... 

31.095 

31.095 

Anterior  and  posterior  princi- 

pal focal  distance  of  lens 

50.617 

39.073 

Distance  of  anterior  principal 

point  of  lens  from  anterior 

surface  of  lens     .... 

2.126 

1.989 

Distance  of  posterior  principal 

point  of  lens  from  poste- 

rior surface  of  lens  .     .     . 

-1.276 

-1.823 

Distance  of  the  two  principal 

points  of  lens  from  each 

0.198 

0.188 

Posterior  principal  focal  dis- 

20.713 

18.689 

Anterior   principal   focal  dis- 

15.498 

13.990 

Distance   from   anterior    sur- 

face of  cornea  to 

First  principal  point  .     .     . 

1.753 

1.858 

Second  principal  point    .     . 

2.106 

2.257 

First  nodal  point    .... 

6.968 

6.566 

Second  nodal  point     .     .     . 

7.321 

6.965 

Anterior  principal  focus      .    • 

—13.745 

-12.132 

Posterior  principal  focus 

22.819 

20.955 

Distance    upon    optical    axis 

from  anterior  surface  of 

cornea  to  retina       .     .     . 

23.0 

23.0 

In  accommodation  a  clear  image  of  an  object  152  mm.  in 
front  of  the  cornea,  or  140  mm.  in  front  of  the  anterior  prin- 
cipal focus,  will  be  formed  upon  the  retina. 


REFRACTION    IN    THE    EYE  463 


Eelations  of  the  Visual  Axis 

It  has  already  been  stated  that  the  refracting 
surfaces  of  the  eye  are  centred,  often  imperfectly, 
upon  a  right  line,  the  optical  axis.  This  line 
normally  meets  the  retina  between  the  yellow 
spot  and  the  optic  papilla  or  exit  of  the  optic 
nerve.  To  see  a  luminous  point  clearly,  the 
image  of  the  point  must  fall  on  the  centre  of  the 
yellow  spot.  The  line  passing  from  the  centre  of 
the  yellow  spot  through  the  nodal  point  to  the 
luminous  point  is  termed  the  visual  axis.  Unless 
the  luminous  point  already  lie  in  the  visual  axis, 
it  must  for  distinct  vision  be  brought  there  by 
the  rotation  of  the  eyeball.  The  object  is  then 
said  to  be  "  fixed  "  by  the  eye.  The  point  about 
which  the  eye  rotates  is  the  centre  of  rotation. 
The  line  between  the  luminous  point  and  the 
centre  of  rotation  is  the  line  of  fixation. 

The  line  of  fixation  and  the  visual  axis  should 
nearly  coincide.  Generally,  the  visual  axis 
and  the  optical  axis  do  not  coincide.  In  other 
words,  the  visual  axis  is  generally  a  secondary 
axis,  and  the  planes  of  the  refracting  surfaces 
are  oblique  to  it.  The  optical  axis  passes  to 
the  inner  side  of  the  yellow  spot.  It  inter- 
sects the  visual  axis  at  the  nodal  point.     Hence 


464  THE   OUTGO    OF   ENERGY 

the  nodal  point  becomes  the  vertex  of  an 
angle,  the  angle  gamma,  7,  the  legs  of  which 
are  the  anterior  portion  of  the  optical  and  visnal 
axes.  The  angle  7  usually  reaches  5°,  but  may 
reach  10°. 

In  emmetropia  and  hypermetropia,  the  visual 
axis  passes  through  the  cornea  on  the  inner  side 
of  the  optical  axis  ;  angle  7  is  then  positive.  The 
eyeball  must  rotate  outwards  in  order  to  fix  an 
object.  Thus  the  visual  axes  seem  to  diverge. 
Hence  the  angle  7  must  be  considered  in  esti- 
mating the  degree  of  a  divergent  squint. 

In  myopia,  the  visual  axis  may  coincide  with 
the  optical  axis  or  pass  through  the  cornea  on 
the  outer  side  of  the  optical  axis.  In  the  latter 
case,  angle  7  is  negative.  In  this  condition  the 
eyeball  must  rotate  inwards  in  order  to  fix  the 
object.  The  deviation  inwards  may  be  confused 
with  convergent  squint. 

Draw  a  diagram  showing  angle  7. 

Visual  Angle.  —  Draw  an  arrow  in  front  of  a 
diagram  of  the  reduced  eye.  Draw  lines  from 
the  nodal  point  through  and  beyond  the  two  ex- 
tremities of  the  object. 

The  angle  included  between  the  lines  drawn 
from  the  nodal  point  to  the  extremities  of  the 
object  is  termed  the  visual  angle. 

Apparent  Size.  — Within  the  lines  marking  the 


REFRACTION    IN    THE    EYE  465 

visual  angle  draw  a  second  arrow  parallel  to  the 
first  and  twice  its  distance  from  the  nodal  point. 
Produce  the  visual  lines  from  the  nodal  point  to 
the  retina. 

Observe  that  the  retinal  images  of  the  large  and 
the  small  arrow  are  of  equal  size.  The  two  ob- 
jects subtend  the  same  visual  angle.  Thus  the 
apparent  size  of  an  object  depends  upon  the  visual 
angle. 

Size  of  Retinal  Image.  —  In  the  emmetropic  eye 
( the  eye  accommodated  for  distant  vision )  the 
size  of  the  object  B  is  to  the  size  of  the  retinal 
image  h  as  the  distance  from  the  object  to  the 
nodal  point  of  the  reduced  eye,  g1}  is  to  the  dis- 
tance from  the  nodal  point  to  the  retina,  g2. 

(5)  B  :  b  : :  g1  :  g2 

The  retinal  image  is  smaller  than  the  object  by 
the  number  of  times  g2  =  15  mm.  is  contained  in 
the  distance,  in  millimetres,  of  the  object  from  the 
nodal  point. 

Calculate  the  size  of  the  retinal  image  of  a 
post  one  metre  high  placed  300  metres  from  the 
observer's  eye. 

Acuteness  of  Vision.  —  Draw  upon  the  visual 
axis  of  the  reduced  eye  a  series  of  arrows  of  equal 
size,  each  bisected  by  the  axis.     Draw  lines  from 

30 


466  THE    OUTGO   OF    ENERGY 

the  extremities  of  these  arrows  to  the  nodal 
point. 

Observe  that  as  the  object  recedes  from  the 
eye  the  visual  angle  and  the  retinal  image  become 
smaller.  When  the  visual "  angle  is  less  than 
one  minute,  the  retinal  image  will  be  too  small 
to  be  perceived ;  the  limit  of  perception  will  be 
reached. 

Smallest  Perceptible  Image.  —  On  a  black  card 
gum  one  millimetre  apart,  and  parallel  with  each 
other,  two  slips  of  white  paper  one  millimetre 
in  width.  "Place  the  card  about  six  metres  in 
front  of  a  window  or  other  sufficient  light.  Face 
the  card  and  move  backward  until  the  millimetre 
space  between  the  two  white  slips  disappears  be- 
cause the  slips  can  no  longer  be  seen  separately. 
Measure  the  distance  gx  from  the  object  to  the 
nodal  point.  Calculate  the  size  of  the  retinal 
image  ( formula  5).  Compare  this  result  with 
the  diameter  of  the  cones  in  the  region  of  dis- 
tinct vision  (page  461). 

Measurement  of  Visual  Acuteness.  —  Taking  V 
as  the  average  smallest  visual  angle  at  which  an 
object  is  perceptible,  Snellen  built  up  a  set  of 
test  letters  by  combining  small  squares  each  of 
which  subtends  an  angle  of  1'.  Thus  the  lines 
of  which  the  letters  are  formed  subtend  an  angle 
of  1'.     The  spaces  between  the  lines  also  subtend 


REFRACTION    IN    THE    EYE  467 

this  angle.  Only  such  letters  are  used  as  can 
be  drawn  approximately  within  a  square  that 
shall  contain  twenty-five  of  the  smaller  squares, 
and  shall  subtend  an  angle  of  5'.  Thus  the 
strokes  and,  so  far  as  possible,  the  spaces  between 
the  strokes  are  one  fifth  the  size  of  the  letter. 
The  size  of  the  letter  the  perception  of  which 
constitutes  normal  vision  at  a  given  distance 
(that  is,  the  letter  that  subtends  a  visual  angle 
of  5'  at  the  given  distance)  is  obtained  by  multi- 
plying the  distance  by  0.001454  mm.,  which  is 
the  tangent 1  of  the  angle  of  5'.  At  the  distance 
of  one  metre  the  size  of  the  standard  letter  is 
1000  X  0.001454  =  1.45  mm.  Near  each  of  Snel- 
len's test  letters  is  recorded  the  distance  viewed 
from  which  the  letter  will  subtend  a  visual  angle 
of  5r  in  the  emmetropic  eye. 

As  some  of  the  letters  are  not  easily  recognized 
by  the  astigmatic  eye  (D,  for  example,  being  some- 
times mistaken  for  B),  the  acuteness  of  vision 
should  not  be  pronounced  normal  unless  each 
letter  of  the  entire  series  can  be  read  at  the  dis- 


1  To  obtain  the  tangent  of  an  angle  draw  a  circle  with  the 
vertex  of  the  angle  as  the  centre.  The  two  legs  of  the  angle 
are  radii  of  the  circle.  Draw  a  perpendicular  (tangent  line) 
from  the  end  of  one  radius  to  the  prolongation  of  the  other. 
Divide  the  length  of  the  perpendicular  by  the  length  of  the 
radius  ;  the  quotient  is  the  function  called  the  tangent  of  the 
angle- 


468  THE    OUTGO    OF    ENERGY 

tance  corresponding  to  the  number  of  the  series. 

d 
The  acuteness  of  vision  is  expressed  by  — ;  where 

d  is  the  greatest  distance  at  which  the  letters 
in  any  line  are  seen  distinctly  by  the  eye  exam- 
ined, and  D  the  distance  at  which  they  can  be 
seen  by  the  normally  acute  eye. 

Place  the  subject  in  a  well-lighted  room  six 
metres  (approximately  20  feet)  in  front  of  a 
card  of  Snellen's  test  types.  Eays  from  an  object 
six  metres  distant  are  practically  parallel.  At 
this   distance   the    letters    numbered  VI  should 

be  read.  If  they  are  clearly  visible,  V  =  -  ;  acute- 
ness of  vision  is  normal.  If  the  subject  at  6  metres 
cannot  see  distinctly  letters  larger  than  those 
marked  XVIII  metres  (approximately  60  feet), 

V  =  — ;   acuteness    of  vision   is   one   third  the 

lo 
normal. 

In  some  eyes  vision  is  so  acute  that  types 
constructed  with  a  visual  angle  of  4  minutes 
(J  the  normal  angle)  can  be  seen  clearly. 


REFRACTION    IN    THE   EYE  469 


Accommodation 


Accommodation.  —  Look  at  any  distant  object. 

The  object  will  be  seen  clearly.  The  (practi- 
cally) parallel  rays  proceeding  from  the  object 
are  brought  to  a  focus  on  the  retina. 

Look  at  an  object  ten  inches  from  the  eye. 

The  rays  proceeding  from  this  object  are  evi- 
dently divergent,  yet  the  object  is  seen  clearly. 
The  divergent  rays  have  also  been  focussed  on 
the  retina.  This  power  of  voluntarily  bringing 
divergent  rays  to  a  focus  on  the  retina  is  termed 
accommodation. 

Schemer's  Experiment.  —  With  a  tine  needle 
pierce  in  a  card  two  holes  at  a  distance  from  each 
other  a  little  less  than  the  diameter  of  the  pupil 
(average  4  mm.).  Hold  the  card  with  the  holes 
horizontal  and  near  the  pupil.  Look  through  the 
holes  at  a  pin  or  needle  held  vertical  about  15  cm. 
(6  inches)  in  front  of  the  eye. 

The  needle  will  be  seen  clearly. 

Move  the  index  finger  over  one  of  the  holes. 

There  will  be  no  change  except  that  the  visual 
field  will  be  darker. 

Fix  a  distant  object,  for  example,  a  cloud. 

The  needle  will  appear  double,  and  each  image 
will  be  rendered  indistinct  by  dispersion  circles. 

Move  the  index  finsjer  over  the  left-hand  hole, 


470  THE   OUTGO    OF    ENERGY 

The  right-hand  image  will  disappear. 

Hold  the  needle  about  100  cm.  away  and  fix 
some  nearer  object.  The  needle  will  appear 
double.     Close  the  left-hand  hole. 

The  left-hand  image  will  disappear. 

Draw  a  diagram  to  explain  these  observations. 
Eemember  that  a  separate  image  of  the  needle 
will  be  formed  by  the  rays  passing  through  each 
hole  in  the  card. 

Dispersion  circles.  —  Place  a  printed  page 
about  two  feet  in  front  of  one  eye,  and  shut  the 
other  eye.  Observe  the  letters  through  a  piece 
of  wire  gauze  held  six  inches  in  front  of  the  eye. 

Either  the  wire  or  the  letters  can  be  distinctly 
seen,  bat  not  both  at  once.  If  the  letters  are 
seen  clearly,  each  wire  will  appear  as  a  broad 
indistinct  line  made  up  of  superposed  dispersion 
circles  and  vice  versa. 

Diameter  of  Circles  of  Dispersion.  —  1 .  If  the 
eye  be  accommodated  for  objects  at  an  infinite 
distance  (practically  twelve  metres  or  more),  the 
image  of  a  near  object  will  fall  behind  the 
retina.  The  image  will  lie  in  the  conjugate  focus 
of  the  object,  and  the  position  of  the  image  can 
be  calculated  by  the  formula  for  conjugate  foci 
(page  444).     From  this  formula  may  be  derived 

y  = 

a 


REFRACTION   IN   THE    EYE  471 

y  =/2  —  F2,  the  distance  from  the  retina  to  the 

image  behind  it. 
g,  the  distance  from  the  anterior  focus  <f>i  to  the 

object. 
(f>l  lies  20  mm.  from  the  nodal  point  K. 
F2  Fv  in  the  reduced  eye,  is  20  x  15  =  300  mm. 
from  K. 

Find  the  distance  behind  the  retina  of  an 
image  whose  object  is  320  mm.  from  K. 

The  distance  is  1  mm. 

2.  If  y  is  known,  the  diameter  of  the  dispersion 
circles  can  be  calculated.  In  the  example  just 
given,  the  pencil  of  rays  diverging  from  each 
luminous  point  in  the  object  was  reunited  in  a 
single  point  one  millimetre  behind  the  retina. 
At  the  retina,  the  converging  cone  had  a  certain 
section,  i.  e.  the  circle  of  dispersion.  The  base  of 
the  cone  is  evidently  the  pupil,  which  in  the 
reduced  eye  is  taken  to  be  19  mm.  in  front  of  the 
retina  and  4  mm.  in  diameter.1 

The  length  of  y  divided  by  the  length  of  the 
whole   cone  (19   mm.),  gives    the  proportion   in 

1  The  diameter  of  the  cone  is  not  precisely  that  of  the  pupil. 
The  rays  in  the  vitreous  would  appear  to  come  from  the  image 
of  the  pupil  formed  by  the  lens.  Thus  the  diameter  changes 
from  4  to  4.23  mm.  At  the  same  time  the  position  of  the  base 
is  changed  from  3.6  mm.  (the  distance  of  the  plane  of  the  pupil 
behind  the  cornea)  to  3.7  behind  the  cornea.  This  brings  the 
base  of  the  cone  19  mm.  in  front  of  the  retina,  which  is  the 
position  assumed  for  it  in  the  reduced  eye. 


472  THE    OUTGO    OF   ENERGY 

which  the  diameter  of  the  cone  at  its  base 
(4  mm.)  is  reduced  at  the  retina.  In  the  example 
taken  y  =  1  mm.  Then  the  proportion  sought  is 
1  '.  19  +  1  =  oV  Thus  the  diameter  of  the  dis- 
persion circle  is  2V  °f  4  mm.  =  J  mm. 

3.  Calculate  the  size  of  the  dispersion  circle 
produced  by  an  object  twelve  metres  from  the 
emmetropic  eye.  At  this  distance  the  dispersion 
circles  are  so  small  as  to  cause  no  perceptible 
lack  of  clearness  in  the  image. 

Accommodation  Line.  —  Hold  a  needle  two 
inches  from  a  printed  page.  Bring  the  eyes  as 
near  the  needle  as  is  possible  without  causing  the 
image  of  the  needle  to  blur.  When  the  needle 
is  at  this  "  near  point "  of  accommodation  it  will 
be  seen  clearly,  but  the  printed  words  will  be 
indistinct.     Draw  back  the  eyes  gradually. 

Soon  a  point  will  be  reached  at  which  both 
needle  and  print  will  be  seen  distinctly.  The 
greatest  distance  between  two  objects  on  the 
visual  line  at  which  the  two  may  both  be  seen 
clearly  while  the  eye  is  accommodated  for  either, 
is  called  the  accommodation  line.  The  length  of 
the  accommodation  line  increases  as  the  object  is 
removed  from  the  eye. 


REFRACTION   IN    THE    EYE 


473 


Mechanism  of  Accommodation 

Narrowing  of  Pupil.  —  1.  Watch  the  pupil  while 
the  subject  accommodates  first  for  a  distant  and 
then  fcr  a  near  object. 

In  accommodation  for  near  objects  the  pupil 
contracts. 

2.  Hold  a  pencil  about  thirty  centimetres  in 
front  of  one  eve.  Close  the  other  eve.  The 
pencil  is  seen  clearly.     Move  the  pencil  towards 


Fig.  66. 


the  eye  until  its  image  becomes  indistinct  from 
dispersion  circles.  Now  observe  the  pencil 
through  a  pin-hole  in  a  card  placed  in  front 
of  the  pupil. 

The  image  is  sharper.  The  size  of  the  dis- 
persion circles  is  diminished  by  making  the 
aperture  smaller  and   thus  cutting  off  the  rays 


474  THE   OUTGO    OF   ENERGY 

that  meet  the  refracting  surfaces  at  a   distance 
from  the  optical  axis  (compare  page  434). 

Relation  of  Iris  to  Lens.  —  1.  Stand  the  convex 
mirror  upright  on  a  level  with  the  eye  of  the 
observer.  Over  the  mirror  (Fig.  66,  C  M)  place 
a  diaphragm  of  black  paper,  I V ,  with  an  aperture, 
P  P',  four  millimetres  in  diameter.  Let  this  aper- 
ture be  the  pupil  and  the  convex  mirror  be  the 
crystalline  lens.  The  wooden  block  in  which  the 
mirror  is  held  will  support  the  diaphragm  so  that 
there  will  be  a  space  between  the  border  of  the 
pupil  and  the  surface  of  the  mirror.  Let  the 
lamp,  L,  be  on  one  side  of  the  aperture  and 
the  observer's  eye,  E,  on  the  other.  By  means 
of  the  convex  lens  of  6.5  cm.  focal  distance  fur- 
nished with  the  ophthalmoscope  concentrate  the 
light  upon  the  margin  of  the  pupil  in  the  direc- 
tion LH.  It  will  pass  the  margin  P  and  be 
reflected  from  the  mirror  to  the  eye  in  the  direc- 
tion H  E.  No  rays  from  L  can  reach  the  mirror 
between  H  and  C.  This  portion  of  the  mirror 
will  reflect  the  posterior  side  of  the  diaphragm. 
Thus  the  light  from  S  falling  on  the  mirror  at  J 
will  Ik;  reflected  in  the  direction  J  E  to  the  ob- 
server's eye,  and  a  dark  band,  the  image  of  the 
back  of  the  diaphragm,  will  appear  in  the  mirror 
between  the  image  of  L  at  H  and  the  margin  of 
the  pupil. 


REFRACTION   IN    THE    EYE  475 

Depress  the  paper  diaphragm  until  the  margin 
of  the  pupil  lies  against  the  mirror.  The  black 
line  will  disappear,  because  the  ray  J  E,  reflected 
from  the  back  of  the  diaphragm,  is  intercepted. 
The  space  P  H  is  closed  (Helmholtz). 

2.  In  a  dark  room  repeat  Experiment  1  upon 
the  eye.  The  iris  will  be  the  diaphragm,  I  V,  and 
the  anterior  surface  of  the  crystalline  lens  will 
be  the  convex  mirror.  The  light  and  the  ob- 
server's eye  should  be  placed  as  in  Fig.  66. 

The  bright  image  of  the  light  formed  by  the 
cornea,  should  be  neglected.  Near  this  image 
are  two  others,  very  much  fainter.  The  larger 
of  the  two  is  indistinct  and  upright ;  it  is  re- 
flected from  the  anterior  surface  of  the  crystal- 
line lens.  The  smaller  is  a  sharp,  inverted  image 
from  the  posterior  surface  of  the  lens.  By  mov- 
ing the  glass  lens  the  light  may  be  thrown  at 
will  on  all  parts  of  the  border  of  the  pupil. 

No  dark  line  or  image  of  the  posterior  surface 
of  the  iris  will  be  seen.  The  maroiu  of  the  iris 
lies  upon  the  lens. 

Changes  in  the  Lens.  —  1.  Direct  the  subject  to 
cover  one  eye.  Place  a  needle  at  the  near  point 
of  the  other  eye  in  line  with  some  distant  object 
that  can  be  clearly  seen.  The  two  objects  must 
be  kept  accurately  in  line  throughout  the  experi- 
ment.    Let  the  observer  stand  at  one  side  of  and 


476  THE   OUTGO   OF   ENERGY 

a  little  behind  the  subject,  so  that  he  shall  see 
about  half  of  the  corneal  image  of  the  black 
pupil  of  the  subject's  eye  projecting  beyond  the 
corneal  border  of  the  sclera.  Note,  from  within 
outwards,  the  optical  section  or  profile  of  the 
margin  of  the  sclera,  the  anterior  half  of  the 
pupil,  a  clear  portion  of  the  cornea,  and  finally 
a  dark  stripe  which  is  the  most  anterior  portion 
of  the  cornea.1 

Watch  carefully  the  clear  interval  between  this 
dark  stripe  and  the  profile  of  the  pupil  while  the 
subject,  keeping  the  eye  steadily  in  one  position, 
accommodates  first  for  the  distant  and  then  for 
the  near  object. 

The  interval  between  the  corneal  stripe  and 
the  border  of  the  pupil  diminishes  on  accommo- 
dation for  near  objects.  Hence  the  border  of  the 
pupil  moves  forward.  If  this  were  not  the  case, 
the  interval  would  become  larger,  for  the  pupil 
narrows  in  accommodation.  Accidental  turning 
of  the  subject's  eye  towards  the  observer  would 
also  cause  the  interval  to  appear  larger.  As  the 
margin  of  the  iris  lies  upon  the  lens,  this  obser- 
vation is  evidence  that  the  anterior  surface  of  the 

1  The  sclera  projects  over  the  iris.  The  inner  surface  of  the 
projecting  portion  is  in  shadow.  The  profile  view  of  the  image 
formed  of  this  projecting  portion  by  the  refraction  of  the  cornea 
is  the  dark  line  observed  in  the  above  experiment.  It  is  dark 
hy  contrast  with  the  image  of  the  welMighted  iris. 


REFRACTION    IN   THE    EYE  477 

lens  moves  forward  in  accommodation  (Helm- 
holtz). 

2.  Place  the  diaphragm  with  L-shaped  aper- 
ture in  the  lantern.  In  a  dark  room  place  the 
lantern  in  front  and  to  the  inner  side  of  the 
subject's  eye,  so  that  the  rays  shall  make  an  angle 
of  about  40°  with  the  visual  axis  of  the  eye 
directed  forwards.  Let  the  observer's  eye  be  in 
a  corresponding  position  to  the  outer  side  of  the 
subject's  eye.  In  the  visual  axis  of  the  subject's 
eye  place  an  object  at  the  near  point  and  one  at 
the  far  point  (six  metres).  Let  the  subject 
accommodate  for  the  far  point. 

Note  the  sharp,  very  bright,  upright  image 
reflected  from  the  cornea,  the  indistinct,  faint, 
upright,  slightly  larger  image  from  the  convex 
anterior  surface  of  the  crystalline  lens,  and  lastly, 
the  sharper,  faint,  inverted,  small  image  reflected 
from  the  concave  posterior  surface  of  the  lens.1 
The  image  from  the  anterior  surface  of  the  lens 
lies  apparently  8-12  mm.  behind  the  pupil,  and 
therefore  disappears  behind  the  border  of  the 
iris  upon  slight  changes  in  the  position  of  the 
light  or  the  observer's  eye.  The  image  from 
the  posterior  surface  lies  apparently  about  1  mm. 

1  These  images  may  be  magnified  with  advantage  by  looking 
at  them  through  the  lens  of  7.5  cm.  focal  distance  furnished 
with  the  ophthalmoscope. 


478  THE    OUTGO    OF   ENERGY 

behind  the  pupil,  and  therefore  is  not  much  dis- 
placed towards  the  pupil  and  the  corneal  image 
upon  slight  movements  of  the  light  or  the  ob- 
server's eye. 

Let  the  subject  accommodate  for  the  near  point. 

The  image  from  the  anterior  surface  of  the 
lens  will  become  considerably  smaller,  and  usually 
it  will  approach  the  middle  of  the  pupil.  The 
image  formed  by  a  convex  mirror  becomes  smaller 
the  smaller  the  radius.  Hence  in  accommoda- 
tion the  anterior  surface  of  the  lens  becomes 
more  convex.1 

The  image  from  the  posterior  surface  also 
becomes  smaller,  but  the  change  is  too  slight 
to  be  observed  by  the  method  employed  in  this 
experiment.  Some  diminution  in  size  would  be 
expected  from  the  shifting  of  the  cardinal  points 
in  accommodation.  Exact  measurements  with 
the  ophthalmometer  show  that  the  change  is  too 
great  to  be  explained  in  this  way. 

Thus  in  accommodation  the  focal  distance  of 
the  lens  is  shortened  and  its  principal  points 
move  forwards. 

1  If  in  accommodation  the  anterior  surface  approached  the 
cornea,  the  image  would  hecome  smaller  through  refraction  in 
the  cornea,  even  though  the  anterior  surface  did  not  become  more 
convex.  Calculation  shows  that  the  change  thus  produced  is 
very  small  relative  to  that  actually  observed  in  the  above 
experiment. 


REFRACTION    IN   THE    EYE  479 


Measurement  of  Accommodation 

Far  Point.  —  The  most  distant  point  of  which 
the  eye  at  rest,  i.  e.  the  ciliary  muscle  entirely 
relaxed,  can  form  a  clear  image  on  the  retina  was 
termed  by  Donders  the  far  point  (ptcnctum  re- 
motum  =  r).  The  distance  of  r  from  the  eye 
=  B.  In  the  emmetropic  eye  parallel  rays  are 
brought  to  a  focus  on  the  retina ;  r  is  theoret- 
ically at  an  infinite  distance.  Practically,  if  the 
accommodation  be  kept  at  rest  by  voluntarily  re- 
laxing the  ciliary  muscle  or  by  paralyzing  the  in- 
nervation of  the  muscle  with  atropine,  the  far 
point  will  be  found  at  twelve  metres,  at  which 
distance  objects  produce  dispersion  circles  so 
small  as  to  cause  no  perceptible  lack  of  clearness 
in  the  image. 

In  the  myopic  eye,  r  is  a  short  distance  in  front 
of  the  eye. 

In  hypermetropia,  only  convergent  rays  can  be 
f ocussed  on  the  retina  of  the  eye  at  rest.  Parallel 
and  divergent  rays  can  be  f ocussed  only  by  use 
of  the  accommodation  mechanism;  r  is  therefore 
negative. 

Determination  of  Far  Point.  —  Place  the  subject 
in  a  well-lighted  room  six  metres  in  front  of  a 
card  of  Snellen's  test-types.     At  this  distance  the 


480  THE    OUTGO    OF   ENERGY 

normal  eye  can  read  the  letters  numbered  VI 
If  the  subject  sees  these  letters  clearly  the  acute- 
ness  of  vision  is  normal,  and  R  is  infinite.  If  the 
subject  reads  I  at  one  metre,  II  at  two  metres, 
but  cannot  read  VI  at  six  metres,  bring  the  test 
card  towards  the  eye  until  a  point  is  reached  at 
which  the  letters  numbered  VI  are  seen  clearly. 
This  is  the  far  point. 

Near  Point. —  1.  Look  through  the  holes  in 
the  card  used  for  Schemer's  experiment  at  a 
needle  placed  vertically  about  30  cm.  (twelve 
inches)  in  front  of  one  eye.  Obtain  a  single 
clear  image  of  the  needle.  Bring  the  needle 
nearer  the  eye.  As  the  distance  between  the 
needle  and  the  eye  becomes  shorter,  the  rays  pro- 
ceeding from  the  needle  become  more  divergent 
and  require  a  greater  convexity  of  the  lens  to 
bring  them  to  a  focus  on  the  retina.  A  point 
will  be  reached  at  which  the  divergence  exceeds 
the  utmost  converging  power  of  the  dioptric  ap- 
paratus and  the  images  received  through  the  two 
holes  in  the  card  can  no  longer  be  made  to  co- 
incide on  the  retina ;  the  needle  will  then  appear 
double.  This  is  the  near  point  of  accommodation 
(punctum  proximum  =  pi).  The  distance  from  p 
to  the  eye  —  P. 

Determination  of  Near  Point.  —  Hold  ill  front  of 
the  eye  a  test  card  containing  print  so  small  that 


REFRACTION    IN   THE    EYE  481 

it  shall  subtend  the  standard  angle  of  5'  when 
placed  25  cm.  from  the  cornea.  The  distance  from 
the  eye  at  which  this  type  can  be  read  clearly 
=  P.  ' 

Range  of  Accommodation.  —  The  range  of  accom- 
modation is  the  expression  of  the  total  accommoda- 
tive power  of  the  eye.  With  the  eye  at  rest  rays 
diverging  from  the  far  point  r  are  brought  to  a 
focus  on  the  retina.  With  the  ciliary  muscle 
fully  contracted,  rays  diverging  from  the  near 
point  p  are  focussed  on  the  retina.  To  bring  the 
more  divergent  rays  from  p  to  the  same  focal 
plane  as  the  less  divergent  rays  from  r,  an  auxiliary 
lens  must  be  employed,  as  hi  the  following  ex- 
periment. 

Place  the  diaphragm  with  L-shaped  aperture 
in  front  of  the  condenser.  Eemove  the  tubes 
holding  the  projecting  lenses.  Bays  will  now 
diverge  from  the  illuminated  I Place  this  illu- 
minated object  at  a  convenient  far  point,  for  ex- 
ample, 26  cm.  in  front  of  the  convex  lens  of  10  cm. 
focal  length.  Place  a  screen  at  the  conjugate 
focus.  Note  the  clear  image.  Move  the  object  8  cm. 
nearer  the  lens.  Let  this  be  the  near  point.  The 
conjugate  focus  now  falls  behind  the  screen  and 
the  image  is  blurred  by  dispersion  circles.  Place 
in  front  of  the  10  D  lens  an  auxiliary  lens  of  +  2 
D.     The  image  will  be  clear.     The  rays  diverg- 

31 


482  THE   OUTGO   OF  ENERGY 

ing  from  the  near  point  will  be  united  by  the  two 
lenses  in  the  same  focal  plane  in  which  the  rays 
diverging  from  the  far  point  were  united  by  the 
first  lens.  The  second  lens  has  "  accommodated  " 
the  optical  system  to  the  distance  R  —  P. 

In  this  experiment  the  power  of  the  +2D  lens 
represents  the  distance  R  —  P,  or  range  of  accom- 
modation. The  power  of  a  lens  is  inversely  pro- 
portional to  its  focal  distance  A.     Consequently, 

the  range  of  accommodation 1  =  1  :  A  or  -r.    Then 

L    1    1 

A~  P~  R 

In  the  eye  the  auxiliary  lens  necessary  for 
focussing  the  rays  diverging  from  the  near  point 
is  provided  by  an  increase  in  the  convexity  of  the 
crystalline  lens.  The  difference  in  refractive 
power  of  the  two  lenses  (the  crystalline  in  its 
least  convex  form  and  the  crystalline  in  its  most 
convex  form)  is  the  measure  of  the  range  of 
accommodation  of  the  eye.  If  the  lens  remain  in 
its  least  convex  form,  an  auxiliary  lens  must  be 
placed  before  the  cornea  in  order  to  bring  rays 
diverging  from  an  object  at  the  near  point  to  a 
focus  on  the  retina.  The  strength  of  this  auxil- 
iary lens  becomes  then  the  practical  measure  of 

1  When  1  =  1  metre. 


REFRACTION   IN   THE    EYE  483 

the   range    of    accommodation,    and    -  =  —  —  — 

A.        Jr       R 

becomes  its  numerical  expression  l 

In   myopia  P  may  be  10  cm.   and  R  25  cm., 

ti         1       10°         inn1       10°        i    -r,      m 

Then  p=ur  =10J)>Tr-25=+I)'  The 

myopia  is  of  4  dioptres,     -r  —  10  D  —  4  D  =  6  D. 

In  this  case  Pis  greater  than  A, 

In  hypermetropia  P  may  be  50  cm.  and  R  neg- 

0K        ™      i    ioo    9r.      ,  1     100 

ative,  —  2o  cm.   I  hen  —  =  -7^=  1 D,  and  —  =  ~^— 

r        5U  ./*;      — zo 

=  -4D.     The  hypermetropia  is  of  4  D.     —  = 

2-(-4)  =  2  +  4rr6D,  which  is  the  sum  of 

P  and  R. 

In  emmetropia  P  may  be  20  cm.   and   R  in- 

1  1        1-      100      rTX      T 

finite.      Then  -.-  =   ~.       -^  =  -^tt  =  o  D.      In 
J.         P       P         20 

1  Theoretically  the  auxiliary  lens  should  be  placed  in  the 
eye  and  not  in  front  of  it,  and  its  second  nodal  point  should 
coincide  with  the  first  nodal  point  of  the  eye.  The  placing  of 
the  auxiliary  lens  in  front  of  the  cornea  alters  the  position  of 
the  cardinal  points  of  the  combined  system,  and  also  alters  the 
focal  distance  of  the  auxiliary  lens.  Rut  the  actual  changes 
in  the  lens  during  accommodation  are  nearly  proportional  to 

—  =  — ,  so  that  the  formula  serves  practically  for  propor- 
tional magnitudes,  i.  e.,  for  comparing  reciprocally  the  different 
values  of  the  range  of  accommodation  under  different  circum- 
stances. 


484 


THE   OUTGO    OF   ENERGY 


other  words,  a  convex  lens  of  5  D  must  be  placed 
before  the  cornea  in  order  to  enable  the  eye  with 
ciliary  muscle  relaxed  to  see  clearly  an  object 
situated  at  the  near  point. 

The  near  point  recedes  as  the  lens  becomes 
harder  with  advancing  age  until  about  the  seven- 
tieth year,  when  B  =  infinity,  and  accommodation 
is  lost. 

RANGE   OF  ACCOMMODATION   AT  DIFFERENT 

AGES 


Age 

P 

P 

in  years. 

in  dioptres. 

in  cm. 

15 

12.0 

8.3 

25 

8.5 

12 

35 

5.5 

18 

45 

3.5 

28 

55 

1.75 

55 

65 

0.75 

133 

70 

0 

00 

Ophthalmoscopy 

Reflection  from  Retina.  —  1.  Copy  the  construc- 
tion used  to  find  the  image  of  the  point  i  formed 
by  the  dioptric  system  C  (page  457).  Assume 
that  the  image  is  itself  luminous,  and  that  rays 


REFRACTION   IN   THE   EYE  485 

in  the  last  medium  are  passing  from  the  image 
to  the  second  (now  the  first)  refracting  surface. 
Find  the  point  at  which  these  rays  unite  in  the 
first  medium  (now  the  second). 

The  rays  will  unite  at  the  original  luminous 
point.  If  the  eye  be  accommodated  £or  a  light 
placed  in  front  of  it,  an  image  of  the  light  will 
be  formed  upon  the  retina.  A  portion  of  the 
light  rays  entering  the  eye  will  be  reflected  from 
this  image.  Passing  back  over  their  original  course, 
they  wTill  form  in  turn  an  image  which  will  ex- 
actly coincide  with  the  luminous  object, 

2.  Draw  a  horizontal  line  as  a  visual  axis. 
Upon  this  visual  axis  draw  two  reduced  eyes, 
normal  size  (Fig.  65),  facing  each  other  a  conven- 
ient distance  apart  (5  cm.).  Let  the  left  be  the 
observer's  eve,  and  the  right  the  eve  of  the  sub- 
ject.  On  the  visual  axis  behind  the  observer's 
eye  draw  a  lamp  flame.  Assume  that  the  sub- 
ject's eye  is  accommodated  for  this  flame. 

The  construction  shows  that  were  the  observ- 
er's eye  away,  an  image  of  the  flame  would  be 
formed  on  the  retina  of  the  subject's  eye.  The 
image  would  reflect  light  toward  the  flame.  This 
reflected  light  would  enter  by  the  observer's 
eye,  and  the  illuminated  area  of  the  subject's 
retina  thus  be  made  visible,  were  it  not  that  the 
observer's  eye  is  necessarily  placed  in  the  visual 


486  THE   OUTGO   OF   ENERGY 

axis,  and  thus  intercepts  the  rays  from  the  source 
of  light  to  the  subject's  eye.  The  interior  of  the 
eye  is  therefore  not  illuminated,  and  the  pupil 
remains  dark. 

3.  Three  millimetres  behind  the  principal 
point  of  each  of  the  two  reduced  eyes  draw  a 
diaphragm  (iris)  with  an  aperture  (pupil)  four 
millimetres  in  diameter.  Assume  that  the  sub- 
ject's eye  is  accommodated  for  the  pupil  of  the 
observer's  eye. 

Note  that  a  dark  image  of  the  pupil  of  the  ob- 
server's eye  will  be  formed  on  the  retina  of  the 
subject's  eye.  The  rays  reflected  from  this  image 
will  form  a  second  dark  image  which  will  exactly 
coincide  with  the  pupil  of  the  observer's  eye. 
Thus  the  observer  will  see  only  the  reflection  of 
his  own  black  pupil  in  the  subject's  eye. 

4.  Throw  light  into  the  subject's  pupil  from  a 
lamp  held  as  near  the  observer's  eye  as  possible. 
The  subject  should  not  look  at  either  the  observer 
or  the  light,  and  his  eye  should  be  accommodated 
for  a  distance  much  less  or  much  greater  than 
that  of  the  observer  or  the  light. 

Part  of  the  pupil  will  appear  red.  It  has  been 
shown  in  Constructions  2  and  3  that  the  pupil  or- 
<  I  i  1 1  arily  appears  black.  When,  however,  a  part  of 
111'-  image  of  the  light  on  the  retina  of  the  subject 
coincides  with  that  of  the  pupil  of  the  observer, 


KEFfi  ACTION   IN  THE   EYE  487 

and  when  the  subject's  eye  is  not  accommodated 
for  either  the  light  or  the  observer  's  pupil,  some 
of  the  light  reflected  from  the  subject's  retina  will 
reach  the  retina  of  the  observer  (Helmholtz). 

Influence  of  Angle  between  Light  and  Visual 
Axis.  —  1.  Draw  a  reduced  eye  with  pupil  of 
four  millimetres  diameter  as  described  above. 
Draw  to  the  margins  of  the  pupil  an  illuminating 
pencil  of  parallel  rays  that  shall  make  with  the 
visual  axis  an  angle  of  about  20°.  Draw  the 
course  of  these  rays  from  the  pupil  to  the  retina 
(seepage  457).  On  the  opposite  side  of  the  visual 
axis  mark  the  nodal  point  of  the  observer's  eye 
in  such  a  position  that  the  observer's  visual  axis 
shall  make  also  an  angle  of  about  20°  with  the 
visual  axis  of  the  subject's  eye.  Draw  rays  from 
this  nodal  point  to  the  pupil,  and  thence  to  their 
focus  on  the  retina. 

The  portion  of  the  interior  of  the  eye  visible 
to  the  observer  will  be  that  included  between 
the  outermost  rays  of  the  two  conical  pencils,  the 
common  base  of  which  is  the  pupil.  Note  that 
the  apex  of  the  cone  is  a  short  distance  behind 
the  nodal  point.  The  visible  portion  includes 
therefore  only  a  part  of  the  anterior  chamber,  a 
small  portion  of  the  lens,  and  a  very  small  por- 
tion of  the  vitreous.1 

1  This  matter  is  clearly  presented  by  Dr.  John  Green  in  his 


488  THE   OUTGO   OF   ENERGY 

2.  Eepeat  Construction  1,  but  bring  the  light 
nearer  the  observer's  eye. 

Diminishing  the  angle  between  the  axis  of  the 
observer's  eye  and  the  axis  of  the  illuminating 
pencil  increases  the  length  of  the  cone  formed  by 
the  intersection  of  the  illuminating  pencil  and 
the  pencil  to  the  observer's  eye.  Thus  the  ob- 
server sees  a  larger  cross-section  of  the  lens  and 
vitreous,  and  sees  farther  into  the  eye. 

3.  Repeat  Construction  1,  but  place  the  ob- 
server's nodal  point  in  the  axis  of  the  illuminat- 
ing pencil. 

The  point  of  the  cone  will  reach  the  retina. 
The  light  reflected  will  emerge  from  the  emme- 
tropic eye  in  parallel  rays  which  will  enter  the 
observer's  eye  and  form  upon  his  retina  an  image 
of  the  illuminated  area  of  the  subject's  retina. 

Influence  of  Size  of  Pupil.  —  Repeat  Construc- 
tion 1  of  the  preceding  section,  but  enlarge  the 
diameter  of  the  pupil  to  eight  millimetres. 

The  visible  portion  of  the  interior  of  the  eye  is 
greater  with  a  large  pupil  than  with  a  small  one. 

Influence  of  Nearness  to  Pupil.  —  Repeat  Con- 
struction 1,  but  draw  the  observer's  eye  nearer  the 
subject's  eye. 

Note  that  rays   from  a  larger  portion  of   the 

article  on  the  Ophthalmoscope  printed  in  the  first  edition  of 
Wood's  Reference  Handbook  of  the  Medical  Sciences. 


REFRACTION   IX   THE   EYE  489 

subject's  retina  enter  the  pupil  of  the  observer 
when  the  eves  are  near. 

Ophthalmoscope.  —  1=  The  eye  of  the  observer 
cannot  be  placed  in  the  axis  of  the  illuminating 
pencil  without  shutting  off  the  illuminating  rays. 
This  difficulty  was  obviated  by  the  invention  of 
the  ophthalmoscope. 

Place  the  electric  lamp  at  the  same  height  as 
the  artificial  eye,  and  a  little  in  front  of  and  to 
one  side  of  it,  so  that  the  axis  of  the  illuminating 
pencil  shall  be  at  right  angles  with  the  visual 
axis  of  the  artificial  eye.  In  front  of  the  artificial 
eye  set  a  clear  glass  plate  at  an  angle  of  45°  to 
the  axis  of  the  illuminating  pencil.  A  portion 
of  the  rays  which  fall  upon  this  plate  will  pass 
through  the  transparent  glass  and  be  lost.  An- 
other portion  will  be  regularly  reflected,  and  will 
be  thrown  into  the  artificial  eye.  A  portion  of 
the  light  returning  from  the  interior  of  the  ob- 
served eye  will  be  reflected  by  the  glass  plate 
and  lost.  Another  portion  will  be  transmitted 
through  the  glass  plate  in  the  direction  of  the 
visual  axis  of  the  observed  eye,  and  may  be 
received  by  the  eye  of  an  observer  placed  in  this 
axis,  as  shown  in  the  preceding  construction 
(Helmholtz). 

2.  Examine  the  Loring  ophthalmoscope.  Its 
essential  parts    are    (1)  the    mirror  of   concave 


490  THE   OUTGO    OF   ENERGY 

glass,  silvered,  pierced  at  its  middle  point  with 
an  aperture  of  about  2.5  mm.,  pivoted  to  turn  to 
either  side  ;  (2)  two  rotating  disks  carrying  a 
series  of  concave  and  convex  lenses  in  front  of 
the  aperture. 

The  silvered  mirror  reflects  more  light  than 
the  mirror  of  transparent  glass.  Further,  it 
allows  the  lamp  to  be  placed  at  the  side  of  the  eye 
to  be  examined,  and  at  any  required  distance  from 
the  mirror.  The  turning  of  the  mirror  upon  a 
pivot  permits  the  more  or  less  oblique  incident 
rays  to  be  thrown  into  the  eye  without  tilting 
the  disks  carrying  the  lenses,  and  thus  rendering 
the  lenses  astigmatic  by  placing  them  at  an 
angle  to  the  optical  axis  which  passes  from  the 
subject's  retina  through  the  aperture  of  the  mir- 
ror and  through  the  lens  behind  the  aperture 
into  the  observer's  eye. 

The  disks  may  be  used  singly  or  in  combi- 
nation. A  series  of  concave  lenses  (marked  — ) 
from  1  D  to  24  D,  and  a  series  of  convex  lenses 
(marked  +)  from  1  D  to  23  D,  are  thus  secured. 

Direct  Method 

Emmetropia.  —  1.  Eemove  from  the  lantern 
the  tubes  holding  the  projecting  lens.  Place  the 
ground  glass  screen   before  the  condenser.     See 


REFRACTION   IN   THE   EYE  491 

that  the  inner  tube  of  the  artificial  eye  is  drawn 
out  to  the  line  marked  zero  upon  its  scale ;  the 
eye  is  then  accommodated  for  distant  vision.  Set 
the  eye  at  the  level  of  the  observer's  eye  and 
near  the  edge  of  the  table.  Place  the  light  on  the 
right  side  of  the  artificial  eye  and  slightly  behind 
it.  Hold  the  ophthalmoscope  in  the  right  hand 
close  to  the  right  eye  at  a  distance  of  about  fifty 
centimetres  from  the  artificial  eye,  and  look 
through  the  aperture  in  the  mirror.  The  elbow 
should  be  close  to  the  side.  The  head  should 
be  vertical  so  that  the  observer's  eye  and  the 
artificial  eye  may  have  the  same  visual  axis. 
Keep  the  reflected  light  upon  the  pupil  of  the 
artificial  eye.  It  will  be  illuminated  by  the  red 
reflection  from  the  choroid  coat.  With  the  pupil 
illuminated,  approach  the  artificial  eye  until  the 
lens-bearing  disk  lies  in  the  anterior  principal 
focus  (50  mm.  in  front  of  this  eye,  13  mm.  in 
front  of  the  cornea  of  the  normal  human  eye; 
seepige!94.)  The  artificial  eye  is  accommodated 
for  distant  objects.  The  observer's  eye  must  also 
be  accommodated  for  distant  vision.  The  power 
of  voluntarily  relaxing  the  ciliary  muscle  is  at- 
tained by  practice  ;  the  observer  should  endeavor 
to  look  through  and  beyond  the  eye  at  some  dis- 
tant object.  If  the  observer  be  myopic  or  hyper- 
metropic, his  refractive  error  should  be  corrected 


492  THE   OUTGO   OF   ENBEGY 

by  placing  the  appropriate  lens  before  the  opening 
in  the  mirror. 

As  the  eye  is  approached,  the  details  of  the 
fundus  will  come  into  view.  Find  the  optic  disk. 
Trace  the  branches  of  the  central  artery  and  vein 
which  perforate  the  disk.  The  image  of  these 
parts  is  virtual,  magnified  about  sixteen  times, 
and  erect. 

2.  Copy  Construction  2,  page  485,  in  which 
two  reduced  eyes  are  placed  on  the  same  visual 
axis  facing  each  other.  At  the  anterior  prin- 
cipal focus  of  the  subject's  eye  draw  a  concave 
mirror  of  175  mm.  focal  distance  with  an  aper- 
ture of  2.5  mm.  through  which  passes  the  visual 
axis. 

The  rays  converging  from  the  mirror  and  pass- 
ing through  the  pupil  are  still  further  converged, 
and  are  brought  to  a  focus  in  the  vitreous, 
whence  they  diverge  to  fall  in  dispersion  circles 
upon  the  retina,  a  large  area  of  which  is  thus 
illuminated. 

Draw  rays  reflected  from  the  retina  to  the 
pupil  of  the  subject's  eye.  They  must  emerge 
from  the  eye  parallel.  Entering  the  observer's 
eye,  with  accommodation  relaxed,  they  will  be 
brought  to  a  focus  on  the  retina.  Show  by  a 
construction  that  the  image  of  the  optic  disk 
formed  in  the  observer's  eye  will  be  inverted  but 


REFRACTION    IN    THE    EYE  493 

will  appear  to  be  upright  and  of  its  natural  size 

(1.5  mm.). 

The  apparent  size  of  this  image  depends  upon 

a  visual   judgment.     The    observer    knows   that 

small  objects  are  usually  held  about  250  mm.  in 

front  of  the  nodal  point.     The  size  of  an  object 

which  at  this  distance  would  give  a  retinal  image 

1.5  mm.  in  diameter,  can  be  found  by  formula  5, 

page  465. 

B  :  1.5  ::  250  :  15 

B  =  25  mm.,  the  apparent  size  of  the  optic 
disk  viewed  by  the  direct  method. 

Ametropia ;  Qualitative  Determination.  —  1. 
Let  an  assistant  make  the  artificial  eye  ametropic 
by  moving  the  draw-tube  until  the  optical  axis  is 
shorter  or  longer  than  normal.  The  observer 
should  not  know  which  form  of  ametropia  has 
been  produced.  Examine  the  retina  with  the 
ophthalmoscope  held  from  30  to  50  cm.  in  front 
of  the  artificial  eye. 

If  the  details  of  the  fundus  can  be  seen,  the 
eye  is  either  myopic  or  hypermetropic. 

Move  the  head  with  the  ophthalmoscope  from 
side  to  side. 

If  the  vessels  appear  to  move  in  the  same 
direction,  the  eye  is  hypermetropic ;  if  in  the 
opposite  direction,  the  eye  is  myopic. 

Measurement   of    Myopia.  —  The    accommoda- 


494  THE    OUTGO   OF   ENERGY 

tion  of  the  observer's  eye  and  the  eye  to  be  ex- 
amined should  be  relaxed.  The  observer's  eye 
must  be  emmetropic ;  if  it  be  myopic  or  hyper- 
metropic, the  defect  should  be  corrected  by  the 
proper  glass  before  the  subject's  myopia  can  be 
measured.  The  correction  may  be  made  with 
spectacles,  or  with  one  of  the  lenses  in  the  disk 
of  the  ophthalmoscope.  The  ophthalmoscope 
should  be  placed  in  the.  anterior  focal  plane  of 
the  eye  examined  (13  mm.  in  front  of  the  cornea 
of  the  human  eye,  50  mm.  in  front  of  the  artifi- 
cial eye).  If  the  observer  cannot  reach  this 
point,  in  examining  the  human  eye,  the  distance 
between  the  correcting  lens  and  the  anterior 
principal  focus  must  be  subtracted  from  the 
focal  distance  of  the  correcting  lens  in  order  to 
find  the  degree  of  hyperrnetropia,  and  be  added 
to  the  focal  distance  of  the  correcting  lens  in 
order  to  find  the  degree  of-  myopia.  Viewed 
from  the  anterior  principal  focus,  the  fundus  will 
be  blurred. 

If  myopia  be  present,  turn  the  disk  until  that 
concave  lens  is  found  which  will  render  clear  the 
image  of  some  one  of  the  vessels  1  near  the  border 
of  the  optic  disk.  The  rays  emerging  from  the 
myopic   eye    are    convergent.     This   lens  makes 

1  The  error  introduced  by  neglecting  the  distance  between  the 
vessels  and  the  nerve  elements  of  the  retina  is  inconsiderable. 


REFRACTION    IN    THE    EYE  495 

them  parallel,  and  its  focal  power  is  the  measure 
of  the  myopia. 

Measurement  of  Hypermetropia.  —  If  the  image 
of  the  fundus  be  blurred  by  hypermetropia,  place 
convex  lenses  before  the  eye  until  the  strongest 
convex  lens  is  found  through  which  the  observer 
can  see  clearly  the  retinal  vessel  or  other  point 
selected.  The  rays  emerging  from  the  hyperme- 
tropic eye  are  divergent.  This  lens  renders 
them  parallel,  and  its  focal  power  is  the  measure 
of  the  hypermetropia. 

Measurement  of  Astigmatism.  —  Set  the  retinal 
tube  of  the  artificial  eye  at  zero.  The  eye  is  now 
emmetropic.  Place  before  the  eye  the  cylindrical 
lens  of  +  2  D.  Examine  the  fundus  with  the 
ophthalmoscope.  The  observer's  accommodation 
must  be  relaxed. 

The  optic  disk  will  no  longer  appear  circular, 
but  will  be  elongated  in  the  direction  of  the 
meridian  of  greatest  curvature.  The  retinal  ves- 
sels will  not  all  be  in  focus.  If  a  horizontal  ves- 
sel be  seen  distinctly,  and  the  vertical  vessel  at 
right  angles  to  it  is  blurred,  the  eye  is  astigmatic 
in  the  horizontal  meridian  (compare  page  423,  and 
remember  that  the  breadth  of  the  image  of  the 
vessel  is  determined  by  means  of  the  rays  passing 
through  that  meridian  of  the  cornea  which  lies  at 
right  angles  to  the  vessel's  course.)    With  the  aid 


496  THE   OUTGO   OF   ENERGY 

of  the  graduated  circle  on  the  front  of  the  artifi- 
cial eye  determine  the  meridian  in  which  the  eye 
is  astigmatic.  Find  the  lens  which  will  make  the 
blurred  vessel  distinct.  If  the  lens,  for  example, 
have  a  focal  power  of  +  2  D,  there  is  simple  hyper- 
metropic astigmatism  of  +  2  D  in  the  given 
meridian.  If  a  lens  of  —  2  D  be  required,  there 
is  simple  myopic  astigmatism  of  —  2  D  in  the 
given  meridian. 

In  compound  astigmatism,  the  eye  is  asymmet- 
rical in  more  than  one  meridian.  Thus  a  clear 
image  of  the  vertical  vessels  may  be  obtained 
with  a  convex  lens  of  +  2  D,  while  the  horizontal 
vessels  may  require  a  lens  of  -f  1  D. 

The  ophthalmoscopic  measurement  of  astigma- 
tism in  the  human  eye  is  exceedingly  difficult, 
and  should  always  be  corrected  by  more  reliable 
methods. 

Indirect  Method 

1.  Arrange  the  light  and  the  artificial  eye  as 
directed  for  the  examination  by  the  direct 
method.  Hold  the  ophthalmoscope  30  cm.  from 
the  artificial  eye.  With  the  other  hand  hold  a 
convex  lens  of  20  D  at  its  own  focal  length  of 
50  mm.  in  front  of  the  cornea.  The  rays  return- 
ing from  the  fundus  pass  through  this  lens  and 
form  an  image  in  the  air  between  the  observer 


REFRACTION   IN   THE   EYE  497 

and  the  lens.  Examine  this  image  through  a 
magnifying  glass  of  +  5  D  placed  behind  the 
aperture  of  the  mirror.  If  the  observer  be 
myopic  in  moderate  degree,  the  aerial  image  will 
lie  near  his  far  point,  and  he  will  need  no  mag- 
nifying or  correcting .  glass ;  if  the  myopia  be 
excessive,  a  weak  concave  glass  should  be  used. 
If  the  observer  be  hypermetropic,  the  degree  of 
his  hypermetropia  should  be  added  to  the  focal 
distance  of  the  magnifying  glass.  The  confusing 
bright  reflexes  from  the  surfaces  of  the  20  D  lens 
may  be  avoided  by  holding  the  lens  slightly 
oblique   to  the  optical  axis. 

The  subject's  eye  and  the  20  D  lens  form  a 
refracting  system  like  the  objective  of  the  com- 
pound microscope;  the  ophthalmoscopic  lens 
plays   the   part   of  the  ocular. 

The  image  is  real,  inverted,  and  magnified. 
But  it  will  appear  to  be  upright.  In  it  all  the 
relations  of  the  retinal  objects  are  reversed.  If 
the  observer  move,  the  image  will  move  in  the 
opposite  direction.  The  size  of  the  image  is  found 
by  formula  5,  p.  61.  B  is  the  size  of  the  aerial 
image,  h  the  size  of  the  optic  disk  —  1.5  mm.,  gx 
the  focal  distance  of  the  20  D  lens  =  50  mm.,  g2 
the  distance  from  the  nodal  point  to  the  retina 
=  15  mm.     Then 

B  :  1.5  : :  50  :  15,  and  B  =  5  mm. 

32 


498  THE   OUTGO   OF   ENERGY 

Thus  the  enlargement  of  the  retinal  details  is 
less  than  with  the  direct  method.  When  the 
aerial  image  is  viewed  through  the  ophthalmo- 
scopic lens  of  -|-  5  D,  an  enlarged  virtual  image 
of  the  first  image  is  formed,  as  in  the  microscope. 
2.  Draw  constructions  showing  the  formation 
of  the  image  in  the  direct  and  indirect  methods. 
Kemember  that  in  the  indirect  method  the  rays 
from  the  mirror  come  to  a  focus  before  reaching 
the  convex  lens.  Their  second  focus  is  in  the 
vitreous. 


vision  499 


X 


VISION 

Mapping  the  Blind  Spot.  —  Fasten  a  rod  fifteen 
inches  from  the  table.  Beneath  the  rod  place 
a  well-lighted  sheet  of  white  paper  (a  page  of 
the  laboratory  note-book  will  serve).  Make  a 
small  black  cross  near  the  left  margin.  Eest 
the  chin  upon  the  rod  in  such  a  way  that  the 
right  eye  shall  look  directly  down  at  the  cross. 
Place  the  hand  over  the  other  eye.  A  straw 
bearing  a  black  pin-head  will  be  drawn  by  an 
assistant  from  the  cross  along  the  horizontal 
meridian  toward  the  temporal  side  of  the  eye 
under  observation.  The  assistant  will  mark  the 
point  where  the  black  object  ceases  to  be  visible, 
and  the  point  at  which  it  reappears.  These  are 
the  boundaries  of  the  blind  spot  of  the  right 
eye  in  the  horizontal  meridian.  Determine  the 
boundaries  in  other  meridians.  Obtain  similarly 
the  outlines  of  the  blind  spot  of  the  left  eye. 

Yellow  Spot.  —  Close  the  eyes  for  half  a 
minute,  and  then  look  at  the  clear  sky  or  a 
brightly  lighted  surface  through  a  solution  of 
chrome  alum  in  a  glass  bottle  with  parallel 
sides.     The  yellow  spot  will  appear  rose-colored 


500  THE   OUTGO   OF   ENEEGY 

in  the  blue-green-red  solution.  The  yellow  pig- 
ment absorbs  some  of  the  blue  and  green  rays. 
The  remaining  rays  form  rose  color. 

Field  of  Vision.  —  Fasten  in  a  vertical  position 
a  sheet  of  white  paper  about  50  cm.  high  and 
60  cm.  broad.  (It  may  be  pinned  to  the  wooden 
stand  set  on  edge  upon  the  electrometer  box.) 
About  20  cm.  from  the  left  margin  and  30  cm. 
from  the  lower  margin  of  the  paper  mark  a  small 
cross.  Let  the  subject  rest  his  chin  upon  a  rod 
clamped  to  the  iron  stand  in  such  a  way  that 
the  right  eye  shall  look  directly  at  the  cross. 
Cement  the  squares  of  black,  red,  green,  and 
blue  papers  to  the  ends  of  separate  straws. 
Carry  the  black  square  from  without  inwards 
along  the  horizontal  meridian  intersecting  the 
cross.  Mark  the  point  at  which  the  black 
object  enters  the  field  of  vision.  This  point  is 
the  temporal  boundary  of  the  visual  field  in  the 
horizontal  meridian.  Determine  in  the  same 
way  the  boundary  on  the  nasal  side.  Eepeat 
for  several  other  meridians.  A  line  joining  the 
points  obtained  will  bound  the  visual  field. 

Determine  the  visual  field  for  red,  green,  and 
blue.  Always  pass  the  test  color  from  without 
inwards.  The  subject  should  be  ignorant  of 
the  color  to  be  used,  and  should  name  the  color 
as  soon  as  it  enters  his  visual  field. 


VISION  501 


Color  Blindness 

The  three  large  skeins  show  the  test  colors. 

1.  Light  Green.  —  Palest  (lightest)  shade  of 
very  pure  green,  —  neither  yellow-green  nor 
blue-green  to  the  normal  eye.  Light  green  is 
chosen  because,  according  to  the  Young-Helm- 
holtz  theory,  it  is  the  whitest  of  the  colors  of 
the  spectrum,  and,  consequently,  is  most  easily 
confused  with  gray.  Light  shades  are  employed 
because  it  is  difficult  to  distinguish  between 
strongly  illuminated  shades. 

2.  Purple  {Rose).  —  A  skein  midway  between 
lightest  and  darkest  purple.  Chosen  because 
purple  combines  two  fundamental  colors  which 
are  normally  never  confounded. 

3.  Red.  —  A  vivid,  slightly  yellowish  red. 
Chosen  because  it  represents  the  color-group  in 
which  red  (orange)  and  violet  (blue)  are  com- 
bined in  nearly  equal  proportions. 

Method  of  Examination  and  Diagnosis.  —  Place 
the  Berlin  worsteds  on  the  white  cloth  in  which 
they  are  wrapped.  They  should  be  well  mixed, 
and  not  spread  out  too  much.  Lay  a  skein  of 
the  first  test-color  in  a  well-lighted  position  two 
or  three  feet  from  the  group.  Inform  the  person 
examined : 


502  THE   OUTGO   OF  ENERGY 

(1)  That  he  must  not  speak  during  the  test. 

(2)  That  the  skeins  are  not  to  be  fingered  or 
tossed  about.  A  skein  should  be  touched  only 
after  its  selection. 

(3)  That  he  must  endeavor  to  pick  out  skeins 
resembling  the  test  skein,  i.  c,  a  little  lighter  or 
darker  in  shade ;  the  resemblance  cannot  be  per- 
fect, as  no  two  shades  are  exactly  alike. 

Green  Test.  —  The  subject  must  pick  out  all 
the  other  skeins  approximately  the  same  shade. 

The  color-blind  selects  some  shade  of  gray. 

Purple  {Rose).  —  The  subject  should  pick  out 
the  skeins  of  the  same  color,  as  before. 

(1)  He  who  is  color-blind  by  the  first  test,  and 
who,  upon  the  second  test,  selects  only  purple 
skeins,  is  incompletely  purple-blind. 

(2)  He  who,  in  the  second  test,  selects  with 
purple  only  blue  and  violet,  or  one  of  them,  is 
completely  red-blind. 

(3)  He  who,  in  the  second  test,  selects  with 
purple  only  green  and  gray,  or  one  of  them,  is 
completely  green-blind. 

Remark.  —  The  red-blind  never  selects  the 
colors  taken  by  the  green-blind,  and  vice  versa. 
Often  the  green-blind  places  a  violet  or  blue 
skein  by  the  side  of  the  green,  but  only  the 
brightest  shades  of  these  colors.  This  does  not 
influence  the  diagnosis. 


vision  503 

Bed.  —  This  test  is  applied  to  those  completely 
color-blind.  Continue  the  test  until  the  person 
examined  has  placed  beside  the  specimen  all  the 
skeins  belonging  to  this  shade,  or  else,  separately, 
one  or  more  "  colors  of  confusion." 

The  red-blind  chooses  (besides  the  red,  green, 
and  brown)  shades  which  to  the  normal  sense 
seem  darker  than  red.  The  green-blind  selects 
opposite  shades,  which  seem  lighter  than  red. 

Violet  Blindness.  —  Very  rare.  Recognized  by 
a  confusion  of  purple,  red,  and  orange,  in  the 
purple  test  (see  2).  Much  care  is  required  to 
diagnosticate  this  form. 

The  Respiration  Scheme.1  —  The  glass  cylinder 
(Fig.  67)  represents  the  thorax.  The  surface  of  the 
water  in  the  glass  cylinder  represents  the  diaphragm, 
and  movable  chest  walls  ;  its  level  may  be  changed 
by  raising  or  lowering  the  large  rubber  tube,  in  the 
free  end  of  which  is  placed  a  second  glass  cylinder, 
not  showu  in  Fig.  67.  The  interior  of  the  cylinder 
above  the  water  represents  the  thoracic  cavity,  and 
the  rubber  balloon  the  lungs.  The  paraffined  cork 
is  pierced  by  a  pleural  and  a  tracheal  tube.  The 
upper  end  of  the  pleural  tube  enters  a  rubber  tube, 
in  the  wall  of  which  is  a  small  hole  closed  by  a  short 
glass  rod.  Through  this  hole  the  pleural  cavity  may 
be  opened  to  the  atmospheric  air.     The  tracheal  tube 

1  American  Journal  of  Physiology,  1904,  x,  p.  xlii. 


504 


THE   OUTGO   OF   ENERGY 


opens  below  into  the  lung,  above  into  a  rubber  tube 
in  the  wall  of  which  is  a  small  opening,  which  repre- 
sents the  glottis,  and  which  may  be  partly  or  wholly 
closed  by  a  glass  rod.  The  left  manometer  shows  the 
intrathoracic  pressure,  the  right  manometer  the  intra- 


Fig.  67.    The  respiration  scheme;  about  one-third  the  actual  size. 


pulmonary  pressure.  The  normal  relations  between 
intrathoracic  and  intrapulmonary  respiration  may  be 
reproduced  with  this  apparatus.  The  pressure  changes 
in  forced  respiration,  obstructed  air  passages,  asphyxia, 
coughing,  sneezing,  hiccough,  and  perforation  of  the 
pleura  may  also  be  studied. 


RESPIRATION  505 

XI     Mechanics  of  Eespiration 

Artificial  Scheme.  —  Eaise  the  left  glass  rod 
above  the  opening  in  the  rubber  tubing  (Fig.  67). 
Hold  the  lower  end  of  the  free  cylinder  even  with 
the  rubber  balloon,  and  pour  in  water  till  the 
level  just  reaches  the  balloon.  Lower  the  left 
glass  rod  to  cover  the  opening. 

The  surface  of  the  water  in  the  attached 
cylinder  represents  the  diaphragm  and  movable 
chest-walls;  the  interior  of  the  cylinder  above 
the  water,  the  thoracic  cavity;  and  the  rubber 
balloon,  the  lungs.  The  left  manometer  shows 
the  intra-thoracic  pressure  ;  the  right  manometer 
shows  the  intra-pulmonary  pressure.  The  left 
glass  rod  closes  the  entrance  to  the  -cylinder, 
i.  e.  makes  the  thoracic  cavity  a  closed  cavity, 
as  is  normal ;  the  right  glass  rod,  with  its  lower 
end  partly  covering  the  opening  in  the  rubber 
tubing,  controls  the  entrance  to  the  balloon  (the 
respiratory  passages). 

Inspiration.  —  Nearly  close  the  respiratory  pas- 
sage. Lower  the  water  level  to  the  base  of  the 
thoracic  cylinder. 

Xote  the  change  in  the  size  of  the  lung,  and 
in  the  pressure  in  the  lung  and  in  the  thorax. 
Give  reasons  for  these  changes. 

Expiration.  —  Widen    the   respiratory    passage 


506  THE    OUTGO    OF    ENERGY 

slightly.  Eaise  the  water  level  slowly  till  the 
lung  is  slightly  but  evenly  distended. 

Note  the  pressure  in  the  pleural  cavity.  Is  it 
positive  or  negative  ?     Why  ? 

Normal  Respiration.  —  Slowly  and  rhythmi- 
cally raise  and  lower  the  diaphragm  (water  level) 
between  the  inspiratory  and  expiratory  level, 
taking  care  that  the  lung  never  becomes  even 
slightly  collapsed  at  the  end  of  expiration. 

Give  reasons  for  the  changes  in  the  intra- 
pulmonary  pressure. 

Forced  Respiration.  —  Eaise  and  lower  the 
diaphragm  more  quickly. 

Observe  that  the  differences  in  pressure  are 
increased. 

Obstructed  Air  Passages. — Diminish  the  inlet 
in  the  respiratory  tube  by  moving  the  glass  plug. 
Raise  and  lower  the  diaphragm. 

The  differences  of  pressure  will  be  increased. 

Asphyxia.  ■ —  Close  the  entrance  to  the  lungs 
entirely. 

Note  the  effect  of  movements  of  the  diaphragm 
upon  the  intra-thoracic  and*  intra-pulmonary 
pressures. 

Coughing  :  Sneezing.  —  Remove  the  glass  rod 
from  the  respiratory  passage.  .  Bring  the  lung  to 
full  inspiration.  Close  the  respiratory  opening 
with  the  moistened  thumb.     Raise  the  diaphragm 


RESPIRATION  507 

half-way  toward  expiration.  Suddenly  open  the 
respiratory  passage. 

Air  is  quickly  and  forcibly  expelled  from  the 
lung  (cough,  sneeze). 

Hiccough.  —  Lower  the  diaphragm  quickly 
toward  full  inspiration,  and  while  the  lung  is 
expanding  close  the  respiratory  opening  with 
the  moistened  thumb  (hiccough). 

Note  the  sudden  changes  of  pressure  in  the 
two  cavities. 

Perforation  of  the  Pleura.  —  Open  the  inlet  to 
the  pleura. 

Note  the  effect  of  the  opening  into  the  pleural 
cavity  upon  the  lung  and  upon  the  intra-pulmo- 
nary  and  intra-thoracic  pressure. 

Observe  the  result  of  movements  of  the 
diaphragm. 


508  THE   OUTGO    OF   ENERGY 


XII 
THE   CIRCULATION   OF   THE   BLOOD 

The  Mechanics  of  the  Circulation 

The  spaces  between  the  cells  of  which  the  body 
is  composed  are  filled  with  a  liquid  called  the 
lymph,  from  which  the  cells  take  their  food  and 
into  which  they  pour  their  waste.  The  materials 
and  the  products  of  metabolism  diffuse  from 
lymph  to  cell  and  from  cell  to  lymph.  In 
animals  in  which  the  division  of  labor  has 
produced  separate  organs  for  digestion,  excre- 
tion, and  the  like,  the  lymph  serves  as  a  medium 
of  exchange.  For  this  purpose  the  relatively 
slow  processes  of  diffusion  are  not  sufficient. 
Food  must  be  more  rapidly  brought  and  waste 
more  rapidly  removed.  A  circulation  must  be 
provided.  There  are  many  ways  in  which  the 
necessary  circulation  is  secured.  In  Cyclops  a 
flow  is  caused  by  movements  of  the  alimentary 
canal.  In  Daphnia,  the  lymph  enters  a  hollow 
muscle  and  is  then  expelled.  In  the  higher 
animals  the  provision  for  rapid  exchange  is  two- 
fold.    The  intercellular  spaces  are  traversed  by  a 


THE    CIRCULATION    OF    THE    BLOOD  509 

countless  number  of  tubes  of  capillary  size,  the 
walls  of  which  are  so  thin  that  substances  in 
solution  pass  through  them  with  great  ease. 
These  capillaries  are  the  ultimate  branches  of 
a  single  tube,  and,  after  fulfilling  their  function, 
the  capillaries  unite  into  a  single  tube  again.  A 
closed  system  is  thus  formed.  This  system  is 
filled  with  a  modified  lymph  called  the  blood, 
which  is  kept  in  constant  circulatioiic  Thus  the 
lymph  in  the  intervascular  spaces  is  in  intimate 
contact  with  a  continually  changing  liquid. 
Further  provision  for  rapid  exchange  is  found 
in  the  circulation  of  the  lymph  itself.  The 
spaces  between  the  cells  are  drained  by  channels 
which  gradually  become  definite  tubes,  the  lym- 
phatics, and  these  finally  join  to  form  two  ducts 
which  empty  into  the  blood  vessels. 

The  unbranched  portion  of  the  vascular  tube 
is  dilated  into  a  cavity  with  thickened  muscular 
walls  termed  the  ventricle  of  the  heart.  The 
ventricle  contracts  rhythmically.  Each  contrac- 
tion raises  the  pressure  in  the  ventricle  until  it  is 
higher  than  the  pressure  in  the  remaining  blood 
vessels.  The  blood  in  the  ventricle  is  thereby 
forced  into  the  blood  vessels  against  the  resist- 
ance of  friction.  The  high  pressure  in  the  ven- 
tricle during  contraction  is  transmitted  into  the 
blood  vessels  and  through  them.     At  each  cross- 


510  THE    OUTGO   OF   ENERGY 

section  of  the  vascular  system  some  of  the  pres- 
sure is  lost  in  overcoming  resistance  ;  hence  the 
pressure  gradually  falls.  The  blood  flows  from 
the  area  of  higher  pressure,  near  the  ventricle,  to 
the  area  of  lower  pressure.  Thus  the  contrac- 
tions of  the  ventricle  establish  a  difference  of 
pressure  in  the  blood  vessels,  which  causes  a 
movement  of  the  contained  liquid. 

At  the  two  points  at  which  the  vascular 
tube  joins  the  ventricle  membranous  valves  are 
placed.  One  of  these  valves  opens  into  the 
ventricle.  It  is  an  inflow  valve.  The  inflow 
valve  closes  when  the  ventricle  contracts.  Con- 
sequently the  contractions  cannot  drive  the 
blood  through  this  orifice.  The  ventricle  can 
drive  the  blood  only  through  the  remaining 
orifice.  Thus  the  ventricle  becomes  a  pump 
and  its  contractions  move  the  blood  always 
in  one  direction.  The  vessels  by  which  the 
blood  is  carried  from  the  ventricle  to  the  cap- 
illaries are  called  arteries ;  those  which  bring 
the  blood  from  the  capillaries  back  to  the  ven- 
tricle are  called  veins.  Adjoining  the  ventricle 
the  great  veins  meet  in  a  common  enlarge- 
ment called  the  auricle.  It  is  at  the  junction  of 
the  auricle  with  the  ventricle  that  the  inflow 
valve  is  placed. 

The  outflow  valve  is  placed  at  that  orifice  of 


THE    CIRCULATION    OF   THE    BLOOD  511 

the  ventricle  which  opens  into  the  arteries. 
When  the  ventricle,  having  by  its  contraction 
raised  the  pressure  in  the  arteries,  begins  to 
relax,  the  pressure  within  its  cavity  becomes  less 
than  that  in  the  arteries.  The  outflow  valve 
then  shuts.  Otherwise  the  arteries  would  be 
placed  in  direct  communication  with  an  area  of 
low  pressure  and  the  relaxation  of  the  ventricle 
would  undo  in  part  the  work  of  the  contraction, 
the  purpose  of  which  was  the  creation  of  a  pres- 
sure in  the  arteries  great  enough  to  force  the 
blood  through  all  the  blood  vessels. 

It  is  obvious  from  these  general  considerations 
that  the  problems  of  the  circulation  are  in  the 
first  instance  those  presented  by  any  system  of 
closed  tubes  through  which  liquid  is  driven  by  a 
pump. 

The  Circulation  Scheme.1  —  The  artificial  scheme 
(Fig.  68)  to  illustrate  the  mechanics  of  the  circulation 
in  the  highest  vertebrates  consists  of  a  pump,  a  sys- 
tem of  elastic  tubes,  and  a  peripheral  resistance.  The 
inlet  and  the  outlet  tubes  of  the  pump  are  furnished 
with  valves  that  permit  a  flow  in  one  direction  only. 
The  peripheral  resistance  is  the  friction  which  the 
liquid  undergoes  in  flowing  through  the  minute  chan- 
nels of  a  piece  of  bamboo.     To  this  must  be  added 

1  Science,  1905,  xxi,  pp.  752-754. 


512 


THE   OUTGO    OF    ENERGY" 


the  slighter   resistance  due   to  friction  in  the  rubber 
and  glass  tubes. 

In  this  system  the  pump  represents  the  left  ven- 
tricle ;  the  valves  in  the  inlet  and  outlet  tubes,  the 


Fig.  68.     Quantitative  circulation  scheme ;  about  one-fourth  the  actual 
size. 

mitral  and  aortic  valves,  respectively  ;  the  resistance 
of  the  channels  in  the  bamboo,  the  resistance  of  the 
small  arteries  and  capillaries.  The  tubes  between 
the  pump  and  the  resistance  are  the  arteries ;  those 
on   the   distal   side  of  the  resistance  are  the  veins. 


THE   CIRCULATION    OF    THE    BLOOD  513 

The  side  branch  substitutes  a  wide  channel  for  the 
narrow  ones,  and  thus  is  equivalent  to  a  dilatation  of 
the  vessels. 

The  pressure  in  the  ventricle  is  varied  through  a 
tambour  covered  with  rubber  membrane.  The  mem- 
brane is  grasped  between  two  disks,  one  below  and 
one  above.  The  upper  disk  is  screwed  down  upon 
the  lower  until  the  membrane  is  tightly  held.  To 
these  disks  is  fastened  a  rod  which  ends  in  a  yoke. 
The  yoke  rests  upon  a  small  wheel,  which  in  turn  is 
supported  by  a  brass  plate  eccentric  in  form.  This 
brass  plate  is  revolved  by  turning  a  handle  attached 
to  the  axle.  As  the  plate  revolves  the  small  wheel 
bears  upon  the  eccentric  rim  and  rises  and  falls  with 
the  rise  and  fall  in  the  rim  of  the  plate.  The  motion 
of  the  small  wheel  is  transferred  through  the  yoke, 
rod,  and  disk  to  the  rubber  membrane,  and  thus  to  the 
interior  of  the  ventricle. 

The  rim  of  the  eccentric  brass  plate  reproduces  the 
intraventricular  pressure  curve  in  the  dog.  In  pro- 
jecting this  curve  upon  the  plate  the  periphery  is 
divided  into  fractions  of  a  second,  and  the  radii  are 
divided  into  millimetres  of  mercury  pressure. 

Each  revolution  of  the  eccentric  plate  reproduces  in 
the  ventricular  tube  both  the  time  and  the  pressure 
relations  of  the  ventricular  cycle  in  the  dog.  The 
intraventricular  pressure  curve  may  be  written  by 
connecting  the  side  tube  with  a  membrane  manometer, 
and  clamping  off  the  arterial  mercury  manometer  to 
be  mentioned  shortly. 

33 


514  THE   OUTGO   OF   ENERGY 

When  the  pressure  rises  in  the  ventricle  to  a  suffi- 
cient height  the  contents  of  the  ventricle  will  be  dis- 
charged through  the  aortic  valve  into  the  aorta,  and 
thus  (through  a  convenient  metal  tube)  into  the 
arterial  tube,  leading  to  the  capillary  resistance. 
Here  two  paths  may  be  taken  :  the  liquid  may  pass 
either  through  the  capillary  channels  in  the  cane,  thus 
meeting  with  a  high  resistance,  or  this  resistance  may 
be  lessened  to  any  desired  degree  by  unscrewing  a 
clamp  and  thus  opening  the  side  tube.  Both  paths 
lead  to  the  venous  tubes,  whence  the  liquid  passes 
through  the  mitral  valve  into  the  ventricle.  The 
mitral  and  aortic  valves  are  of  a  modified  Williams 
type.  Metal  tubes  closed  at  one  end  conduct  the 
liquid  respectively  to  or  from  the  ventricle.  The 
liquid  enters  or  leaves  the  valve-tube  through  a 
hole  covered  by  a  rubber  valve-flap,  not  shown  in 
Fig.  68.  Each  valve  is  surrounded  by  a  glass  tube 
through  which  the  working  of  the  valve  may  be 
inspected. 

Mercury  manometers  measure  the  pressure  in  the 
arteries  and  veins  near  the  capillary  resistance.  The 
arterial  manometer  is  provided  with  a  glass  thistle- 
tube  to  catch  any  mercury  that  may  be  driven  out  by 
a  careless  operator. 

If  the  arterial  mercury  manometer  be  replaced  by  a 
membrane  manometer,  or  if  it  be  provided  with  a  float 
and  writing  point  arterial-pressure  curves  may  be  writ- 
ten, identical  with  those  obtained  from  the  carotid 
artery  of  the  dog. 


THE   CIRCULATION    OF   THE    BLOOD  515 

Normal  sphygmographic  tracings  may  be  obtained 
by  using  a  sphygmograph  on  the  aortic  tube. 

Palpation  of  the  arterial  tube  will  give  a  pulse  the 
"feel"  of  which  cannot  be  distinguished  from  that  of 
the  pulse  in  the  normal  subject ;  the  pressure  waves 
in  the  quantitative  scheme  and  in  the  living  animal 
are  identical  in  respect  of  both  time  and  pressure. 

The  Conversion  of  the  Intermittent  into  a 
Continuous  Flow 

When  a  pump  forces  water  or  any  other 
incompressible  fluid  through  tubes  with  rigid 
walls,  the  inflow  and  outflow  are  equal  and  in  the 
same  time.  The  outflow  ceases  the  instant  the 
inflow  ceases.  The  same  is  true  in  a  system  of 
elastic  tubes  so  short  and  wide  that  friction  be- 
tween the  liquid  and  the  walls  causes  practically 
no  resistance  to  the  flow.  Here  the  quantity 
received  from  the  pump  can  still  escape  from  the 
distal  end  of  the  system  during  the  stroke  of  the 
pump.  When  the  resistance  is  increased  by 
narrowing  the  tubes,  or  by  increasing  their 
length,  or  in  both  these  ways,  not  all  the  liquid 
received  from  the  pump  can  pass  by  the  resist- 
ance during  the  stroke  of  the  pump,  —  the  re- 
mainder must  pass  during  the  interval  between 
one  stroke  and  the  next.  The  portion  which 
cannot   pass   during    the   stroke  finds    room  be- 


516  THE    OUTGO    OF   ENERGY 

tween  the  pump  and  the  resistance  in  the  dilata- 
tion of  the  containing  vessels.  To  effect  the 
dilatation  the  force  or  pressure  transmitted  from 
the  pump  presses  out  the  vessel  walls  until  this 
pressure  is  held  in  equilibrium  by  the  elastic  re- 
action of  the  walls.  As  the  pressure  from  the 
pump  wanes,  the  energy  stored  by  it  in  the  ten- 
sion of  the  vessel  walls  is  reconverted  into 
mechanical  motion,  and  the  walls  return  towards 
their  original  position,  driving  the  liquid  out  of 
the  tube  past  the  resistance. 

1.  Open  the  side  branch  by  unscrewing  the 
pressure-clip.  See  that  the  tubes  are  well  filled 
with  water.  Make  a  single  brief  gentle  pressure 
on  the  ventricle. 

Note  (1)  that  practically  ail  the  liquid  driven 
out  by  the  stroke  escapes  through  the  side 
branch,  in  which  the  resistance  is  low,  rather 
than  through  the  high  capillary  resistance. 
(2)  Only  a  portion  of  the  liquid  escapes  during 
the  stroke.  (3)  The  portion  which  cannot 
escape  by  the  resistance  during  the  stroke  finds 
space  in  a  very  evident  dilatation  of  the  tubes 
nearer  the  pump,  i.  e.  between  the  pump  and 
the  principal  resistance.  (4)  A  membrane  ma- 
nometer coupled  to  the  side  tube  of  the  ventricle 
would  show  a  sudden  rise  and  fall  indicating 
a  sudden  rise  and  fall  in  the  intraventricular 
pressure.      (5)  Close  observation  shows  that  on 


THE    CIRCULATION    OF   THE    BLOOD  517 

the  stroke  of  the  pump  the  tubing  just  distal  to 
the  aortic  valve  begins  to  expand  sooner  than 
that  farther  away.  Evidently  the  change  of 
pressure  produced  by  the  stroke  of  the  pump  is 
transmitted  from  point  to  point  through  the 
liquid  in  the  tubes.  (6)  The  arterial  manometer 
shows  a  sudden  rise  and  fall.  Observe  that  the 
rise  is  not  synchronous  with  the  stroke  of  the 
pump,  but  begins  an  instant  later.  This  interval 
is  occupied  by  the  transmission  of  the  pressure 
change  from  the  pump  to  the  mercury  column, 
and  in  part  by  the  time  required  to  overcome  the 
inertia  of  position  of  the  mercury.  The  oscilla- 
tions of  the  mercury  following  the  primary  rise 
and  fall  are  due  to  inertia.  (7)  Observe  the  action 
of  the  valves  (they  consist  of  a  metal  tube,  closed 
at  one  end,  and  pierced  with  a  hole  which  is 
covered  with  a  rubber  flap  tied  on  both  sides  of 
the  hole).  (8)  Place  a  finger  on  the  "aorta" 
near  the  valve  and  note  the  pressure  wave  (pulse) 
as  it  passes  along  the  vessel. 

2.  With  the  side  branch  open  as  in  Experiment 
1,  compress  the  bulb  rhythmically  and  gradually 
increase  the  frequency  of  stroke. 

It  will  be  found  that  at  about  twenty  strokes 
to  the  minute  the  stream  will  be  intermittent. 
As  the  interval  between  the  strokes  is  shortened 
the  liquid  received   from  the   pump  in  any  one 


518  THE   OUTGO   OF    ENERGY 

stroke  cannot  all  escape  by  the  resistance  during 
the  stroke  and  the  succeeding  interval.  The 
next  stroke  comes  before  the  outflow  from  the 
preceding  stroke  is  finished,  and  the  stream  be- 
comes remittent. 

Still  further  increase  the  frequency  of  the 
stroke.  A  rate  will  be  reached  at  which  one- 
half  the  quantity  received  from  the  pump  will 
pass  by  the  resistance  during  the  stroke  of  the 
pump  and  the  remaining  half  will  pass  in  the 
interval  between  that  stroke  and  the  next ; 
the  intermittent  will  be  converted  into  a  con- 
tinuous flow. 

Observe  that  the  duration  of  the  intervals  is 
greater  than  the  duration  of  the  strokes  of  the 
pump.  Thus  the  time  during  which  the  circula- 
tion is  carried  on  by  the  energy  stored  by  the 
pump  in  the  elastic  walls  of  the  vessel  is  greater 
than  the  time  during  which  it  is  carried  on  by 
the  direct  stroke  of  the  pump. 

Note  that  the  arterial  pressure  remains  low 
even  after  the  stream  becomes  continuous.  An 
increase  in  the  frequency  of  the  beat  has  little 
influence  on  the  blood  pressure  where  the  peri- 
pheral resistance  is  very  slight. 

3.  Close  the  side  branch,  so  that  the  liquid 
must  pass  through  a  high  peripheral  resistance. 
Compress  the  bulb  at  such  a  rate  that  the  outflow 
shall  be  continuous. 


THE    CIRCULATION    OF   THE    BLOOD  519 

The  frequency  require!  to  make  the  flow  con- 
tinuous is  now  much  less  than  when  the  peri- 
pheral resistance  was  low. 


The  Eelation  between  Eate  of  Flow  and 
Width  of  Bed 

In  a  frog  slightly  paralyzed  with  curare  destroy 
the  brain  by  pithing,  with  the  least  possible  loss 
of  blood.  Lay  the  frog  back  down  on  the  mes- 
entery board.  Open  the  abdomen  in  the  median 
line.  Draw  the  intestine  over  the  cover  glass 
upon  the  cork  ring  so  that  the  mesentery  may 
lie  upon  the  glass  evenly  and  without  stretch- 
ing. The  mesentery  must  be  kept  constantly 
moist  with  normal  saline  solution.  Examine 
the  blood  vessels  in  the  mesentery  with  No.  3 
Leitz  objective. 

Note  the  swift  flow  in  the  larger  vessels  and 
the  slow  movement  of  the  blood  through  the 
capillaries. 

The  combined  cross-sections  of  the  capillaries  in 
the  body  are  vastly  greater  than  the  cross-section 
of  the  arteries  or  the  veins.  The  total  quantity 
of  blood  passing  in  a  unit  of  time  through  the 
arteries  or  veins  and  the  capillaries  is  the  same. 
If  less  passed  through  the  capillaries  than  through 
the  arteries,  the  capillaries  would  soon  be  gorged 


520  THE   OUTGO    OF   ENERGY 

to  bursting.  If  more,  the  arteries  would  soon  be 
empty.  As  the  quantity  passing  through  the 
capillaries  and  the  arteries  and  veins  in  a  unit  of 
time  must  thus  be  the  same,  it  follows  that  where 
the'  combined  cross-section  of  the  channel  or 
"  bed  "  is  small,  the  blood  must  flow  faster  than 
where  the  cross-section  is  large.  A  river  rushes 
rapidly  through  a  gorge,  but  moves  sluggishly 
where  meadow-lands  afford  a  wider  channel. 
Thus  the  blood  flows  with  great  velocity  in  the 
great  arteries,  less  rapidly  in  their  branches,  and 
very  slowly  indeed  in  the  capillaries,  the  com- 
bined width  of  which  is  so  great  compared  to 
that  of  the  arteries.  And  as  the  capillaries  unite 
into  the  smaller  veins,  and  these  into  the  larger 
veins,  the  combined  cross-section  or  bed  becomes 
ever  smaller  and  the  blood  moves  ever  more 
swiftly.  Were  the  slow  passage  of  the  blood  in 
the  capillaries  due  simply  to  friction,  the  blood 
would  move  still  more  slowly  in  the  veins  be- 
cause the  retarding  influence  of  the  friction  in 
the  veins  would  be  added  to  that  of  the  capillaries. 
There  is  an  inverse  relation  between  the  rate  of 
flow  and  the  area  of  bed. 


the  circulation  of  the  blood        521 
The  Blood- Pressure 

The  Relation  of  Peripheral  Resistance  to  Blood- 
Pressure.  —  Revolve  the  disk  of  the  artificial 
scheme  at  a  rate  that  will  produce  a  continuous 
outflow. 

With  each  successive  stroke  the  portion  of 
liquid  unable  to  pass  the  resistance  during  the 
stroke  and  the  succeeding  interval  is  added  to 
that  left  behind  from  preceding  strokes.  The 
arteries  become  more  and  more  full.  The  arte- 
rial manometer  registers  a  higher  and  higher 
pressure.  At  length  the  pressure  ceases  to  rise. 
The  mercury  remains  at  a  mean  level  broken  by 
a  slight  accession  at  each  stroke.  The  pump 
now  merely  maintains  the  constant  high  arterial 
pressure.  This  pressure  suffices  to  drive  through 
the  resistance  during  each  stroke  and  the  sue- 
ceeding  interval  all  the  liquid  received  from  the 
pump  during  the  stroke. 

The  venous  pressure  remains  very  low.  The 
capillary  resistance  (to  which  must  especially  be 
added  the  resistance  of  the  smallest  arteries) 
almost  entirely  exhausts  the  pressure  in  the 
arteries.  Hence  the  sudden  and  profound  dif- 
ference observed  between  the  arterial  and  the 
venous  pressure.  A  second  arterial  manometer 
placed    near    the   aorta   would    show   that    the 


522  THE   OUTGO   OF   ENERGY 

loss  of  pressure  between  the  ventricle  and  the 
smallest  arteries  is  relatively  slight. 

The  pulse  is  absent  on  the  venous  side  of  the 
resistance. 

The  Curve  of  Arterial  Pressure  in  the  Frog.  — 
Expose  the  heart  of  a  frog,  the  brain  of  which  has 
been  pithed  without  haemorrhage.  Provide  a  fine 
cannula  with  a  short  piece  of  rubber  tubing. 
Fill  cannula  and  tube  with  one  per  cent  sodic  car- 
bonate solution,  and  close  the  end  of  the  tube  with 
a  small  glass  rod.  Tie  a  ligature  about  one  aorta 
as  far  as  possible  from  the  junction  of  the  two 
aortas.  Knot  the  ends  of  the  ligature  together. 
Pass  a  second  ligature  beneath  the  same  aorta,  but 
do  not  tie  it.  Lift  the  vessel  by  the  second 
ligature  so  that  the  vessel  is  constricted  by  lying 
across  the  thread.  Between  the  two  ligatures 
open  the  aorta  with  sharp  scissors  and  introduce 
the  cannula.  Fasten  the  cannula  in  place  by 
means  of  the  ligature.  Place  the  frog-board  on 
the  wooden  stand  to  bring  the  heart  on  a  level 
slightly  higher  than  the  level  of  the  mercury  in 
the  mercury  manometer  (Fig.  69).  See  that  the 
proximal  limb  of  the  manometer  is  filled  with 
one  per  cent  sodic  carbonate  solution  to  the  ex- 
clusion of  air.  Bring  the  writing  point  of  the 
manometer  against  a  smoked  drum  and  revolve 
the  drum  once  by  hand  to  record  a  line  of  atmos- 


THE   CIRCULATION   OF   THE   BLOOD 


523 


pheric  pressure.  Close  the  aorta  containing  the 
cannula  by  gentle  pressure  with  a  forceps  the 
blades  of  which  are  covered  with  rubber  tubincr. 

o 

Join  the  cannula-tube  to  the  manometer,  exclud- 
ing air  bubbles.     Remove  the  forceps. 

The  mercury  will  fall  in  the  proximal  and  rise 
in  the  distal  limb  until  the  blood-pressure  in  the 
aorta  is  balanced  by  the  column  of  mercury. 
With  each  ventricular  beat, 
the  column  rises  a  short  dis- 
tance above  the  mean  level 
and  sinks  again. 

Record  the  blood-pressure 
curve  on  a  very  slowly 
moving  drum.  To  get  the 
actual  pressure  in  milli- 
metres of  mercury  multiply 
by  two  the  mean  height  of 
the  curve  above  the  atmos- 
pheric pressure  line. 

The  Effect  on  Blood-Pressure  of  Increasing  the 
Peripheral  Resistance  in  the  Frog.  —  The  peri- 
pheral resistance  may  be  increased  by  the  nar- 
rowing of  the  small  arteries  which  follows  the 
stimulation  of  special  vaso-constrictor  nerve  fibres. 
The  vaso-constrictor  nerves  may  be  stimulated 
directly  or  reflexly.  The  latter  method  is  chosen 
here. 


Fig.  69.     The  small  mercury 
manometer. 


524  THE    OUTGO   OF   ENERGY 

Expose  the  sciatic  nerve.  Tie  a  ligature  about 
the  nerve  near  the  distal  end  of  the  wound,  and 
sever  the  nerve  on  the  distal  side  of  the  ligature. 
Stimulate  the  central  end  with  a  tetanizing 
current  of  moderate  strength. 

The  afferent  impulses  set  up  by  the  stimula- 
tion proceed  to  the  spinal  cord  and  thence  to  the 
bulb,  where  they  excite  nerve  cells  which  dis- 
charge impulses  that  cause  the  smaller  arteries 
(and  probably  the  veins)  to  constrict.  This 
narrowing  causes  the  arterial  pressure  to  rise. 

Changes  in  the  Stroke  of  the  Pump ;  Inhibition 
of  the  Ventricle.  —  While  the  arterial  pressure  in 
the  artificial  scheme  is  at  a  good  height  (120  mm. 
Hg)  arrest  the  ventricular  stroke  (the  ventricle 
in  animals  may  be  thus  inhibited  by  stimula- 
tion of  the  vagus  nerve,  page  316). 

So  soon  as  the  ventricle  ceases  to  beat,  the  less 
distended  arteries  will  empty  themselves  through 
the  peripheral  resistance,  and  the  arterial  man- 
ometer will  show  a  continuous  fall  in  blood- 
pressure. 

Resume  the  ventricular  beats. 

The  mercury  in  the  arterial  manometer  will 
rise  in  large  leaps,  corresponding  to  the  ease  with 
which  the  early  strokes  of  the  pump  distend  the 
lax  arteries  (the  inertia  of  the  mercury  somewhat 
exaggerates   the   rise   at  each    stroke).      As  the 


THE   CIRCULATION   OF   THE    BLOOD  525 

blood-pressure  rises,  however,  the  excursion  of 
the  mercury  for  each  ventricular  stroke  becomes 
less  and  less,  corresponding  to  the  smaller  and 
smaller  difference  between  the  pressure  in  the 
arteries  and  the  maximum  pressure  within  the 
ventricle,  until  at  length  equilibrium  is  restored 
between  the  peripheral  resistance  and  the  force 
and  frequency  of  the  ventricular  beat. 

The  Effect  of  Inhibition  of  the  Heart  on  the 
Blood-Pressure  in  the  Frog.  —  Arrange  an  induc- 
torium  for  strong  tetanizing  currents.  Insert 
the  electromagnetic  signal  in  the  primary  circuit 
and  bring  its  writing  point  beneath  that  of  the 
manometer.  Eaise  the  heart  gently.  Note  the 
white  "crescent"  between  the  sinus  venosus  and 
the  right  auricle.  Put  the  points  of  the  elec- 
trodes on  the  crescent,  and  close  the  circuit 
for  a  moment.  After  one  or  two  beats  the 
heart  will  stop. 

Observe  the  great  fall  in  blood-pressure. 
Cease  the  stimulation. 

The  mercury  returns  in  leaps  to  its  former 
level. 

The  Heart  as  a  Pump 

The  Opening  and  Closing  of  the  Valves.  —  Secure 
a  high  arterial  pressure  (120  mm.  Hg)  in  the 
artificial   scheme.     Now  greatly  slow  each  ven- 


526  THE    OUTGO    OF    ENERGY 

tricular   beat    and   at    once   observe   closely    the 
action  of  the  valves. 

It  will  be  seen  that  the  mitral  valve  closes  as 
soon  as  the  ventricle  begins  to  contract,  but  the 
aortic  valve  does  not  open  until  the  intraventric- 
ular pressure  has  risen  above  that  in  the  aorta. 
Time  is  required  for  this  rise  in  the  pressure  in 
the  ventricle.  During  this  period  both  mitral 
and  aortic  valves  are  closed.  When  the  ventri- 
cle begins  to  relax,  the  intraventricular  pressure 
speedily  falls  below  that  in  the  aorta,  and  the 
aortic  valve  shuts,  but  the  intraventricular  pres- 
sure normally  must  fall  at  least  100  mm.  Hg 
farther  before  it  shall  be  lower  than  that  in  the 
auricle.  During  this  fall  all  the  heart  valves  are 
again  closed ;  the  aortic  valves  are  already  shut, 
and  the  mitral  not  yet  open. 

The  Period  of  Outflow  from  the  Ventricle.  —  Tie 
a  rubber  membrane  over  the  smaller  thistle-tube 
of  the  sphygmograph  (Fig.  70)  and  cement  a  bone 
button  in  the  centre.  Connect  a  membrane  ma- 
nometer :  with  the  side  tube  of  the  ventricle. 
Bring  the  writing  points  of  the  recording  tam- 

1  If  such  a  manometer  is  not  at  hand,  carry  a  thin  wire  from 
the  yoke  of  the  disk  of  the  circulation  scheme  to  a  light  muscle 
lever,  counterweighted  from  the  pulley  or  pulled  gently  upward 
by  a  rubber  band  attached  to  the  lever.  This  lever  will  record 
the  up  and  down  movement  of  the  disk  and  thus  mark  the 
beginning  of  the  ventricular  stroke. 


THE   CIRCULATION    OF   THE    BLOOD 


527 


boui  and  the  manometer  into  the  same  vertical 
line  against  a  smoked  drum.  Let  the  drum  re- 
volve at  a  fast  speed. 

Place  the  button  of  the  receiving  tambour  on 
the  aorta.  It  will  record  the  aortic  pulse  and 
the  membrane 
manometer  will 
record  the  intra- 
ventricular pres- 
sure. Let  the 
ventricle  pump 
with  the  usual 
force  and  fre- 
quency. When 
the  two  curves 
have  been  writ- 
ten   stop     the 

clockwork  and  turn  back  the  drum  until  the 
point  of  the  lever  recording  the  ventricular  pres- 
sure lies  at  the  exact  beginning  of  the  upstroke 
in  the  aortic  pulse  curve.  Cause  each  lever  to 
write  an  ordinate  on  the  stationary  drum.  These 
ordinates  will  indicate  synchronous  points  and 
will  mark  the  beginning  of  the  "outflow"  period. 

The   Sphygmograph   Tambour.1  —  This  small  and 
very  sensitive  tambour   (Fig.  71)  is  mounted  upon  a 

1  First  Catalogue  of  Harvard  Physiological  Apparatus,  1901, 
p.  47. 


Fig.  70.     The  sphygmograph. 


523 


THE   OUTGO   OF   ENERGY 


hollow  tube  through  which  the  air  waves  reach  the 
rubber  ruerabraue.  A  right-angled  piece  of  alumin- 
ium transmits  the  motion  of  the  membrane  to  the 
writing  lever.     The  moving  parts  are  of  the  lightest 


Fig.  71.     The  sphygmograrih  tambour ;  about  twice 
the  actual  sLse. 


construction.  The  axle  of  the  writing  lever  is  held  in 
a  yoke,  the  distance  of  which  from  the  fulcrum  of  the 
lever  is  readily  adjustable.  The  rubber  membrane  is 
not  tied,  but  is  held  in  place  by  a  removable  ring,  — 
a  time-saving  device. 

If  a  small  glass  thistle-tube  placed  over  the  carotid 
artery  be  connected  with  this  tambour  by  a  rubber 
tube,  preferably  with  a  side  branch,  admirable  pulse 
tracings  may  be  recorded.  By  covering  the  thistle- 
tube  with  a  rubber  membrane  upon  which  a  bone  but- 
ton is  cemented,  sphygmograms  may  be  taken  from 
the  radial  artery  or  from  the  tubes  of  the  circulation 
scheme.  The  same  tambour  is  used  with  the  plethys- 
mograph  tube. 


THE   CIRCULATION    OF   THE    BLOOD  529 

Now  turn  the  drum  until  the  point  of  the 
aortic  lever  lies  beneath  the  notch  seen  in  the 
down  stroke  of  the  pulse  curve  (the  dicrotic 
notch,  see  page  546).  Describe  synchronous 
ordinates.  It  is  known  that  the  dicrotic  notch 
in  the  aortic  pulse  curve  corresponds  closely  to 
the  moment  of  closure  of  the  aortic  valves.  It 
marks,  therefore,  the  end  of  the  outflow  period. 
Note  that  this  point  is  reached  soon  after  the 
ventricle  begins  to  relax.  Thus  the  period  dur- 
ing which  the  intraventricular  pressure  is  higher 
than  the  pressure  in  the  aorta  embraces  part  of 
the  relaxation  as  well  as  part  of  the  contraction 
of  the  ventricle.  It  includes  approximately  the 
highest  third  of  the  intraventricular  pressure 
curve. 

Observe  also  the  considerable  interval  between 
the  beginning;  of  ventricular  contraction  and  the 
opening  of  the  aortic  valve,  as  shown  by  the 
upstroke  in  the  pulse  curve  consequent  upon 
the  entrance  of  liquid  into  the  aorta. 

The  Visible  Change  in  Form.  —  Expose  the  heart 
of  a  frog;.  Observe  the  Great  veins,  the  auricles, 
the  single  ventricle,  the  two  aortas,  and  the  dila- 
tation, or  bulbus,  by  which  the  aortas  are  con- 
nected with  the  ventricle.  All  these  parts  except 
the  two  aortse  are  contracting.  The  veins  con- 
tract first ;  the  auricles  next ;  then  the  ventricle ; 

34 


530  THE    OUTGO    OF   ENERGY 

last  the  bulbus.  Note  the  pallor  of  the  contracted, 
empty  ventricle. 

Graphic  Record  of  Ventricular  Contraction.  — 
Pass  a  fine  wire  through  the  tip  of  the  ventricle 
and  fasten  the  free  end  to  the  heart  lever  (Fig.  53). 
Let  the  lever  write  on  a  slow-moving  drum. 

Note  the  characteristics  of  the  curve. 


The  Heart  Muscle 

All  Contractions  Maximal.  —  Inhibit  the  heart 
by  a  Stannius  ligature  (see  page  562).  Find  the 
least  strength  of  stimulus  that  will  cause  the  ven- 
tricle to  contract.  Increase  the  strength  of  the 
stimulus,  but  do  not  stimulate  oftener  than  once 
in  ten  seconds  (to  avoid  the  staircase  contractions 
described  below). 

The  force  of  ventricular  contraction  will  re- 
main the  same,  notwithstanding  the  increased 
stimulus. 

If  the  heart  responds  at  all  to  a  stimulus,  it 
responds  by  a  maximum  contraction.  There  is 
no  interval  between  the  minimal  and  maximal 
value  (compare  page  175). 

Staircase  Contractions.  —  Find  the  least  stimu- 
lus  that   will  cause    the   ventricle   to   contract. 


THE   CIRCULATION    OF   THE    BLOOD  531 

Kepeat  this  minimal  stimulus  every  5  seconds, 
recording  the  contractions  on  a  drum  turned 
about  5  mm.  by  hand  after  each  contraction. 

The  contractions  of  the  ventricle  will  be  suc- 
cessively stronger,  so  that  the  apices  of  the  curves 
will  form  an  ascending -line  ("  staircase  ").  The 
form  of  the  staircase  is  always  an  hyperbola. 
Successively  stronger  responses  to  repeated  stim- 
uli of  uniform  strength  can  also  be  obtained 
from  the  curarized  gastrocnemius  of  the  frog, 
perfused  with  blood,  and  from  mammalian  and 
invertebrate  muscles.  The  contraction  appears  to 
increase  the  irritability.  Thus  the  same  stimu- 
lus causes  a  greater  contraction  after  a  brief 
tetanus  than  before.  Rossbach  and  Bohr  have 
observed  this  after-effect  continuing  more  than 
thirty  minutes. 

The  Isolated  Apex ;  Bernstein's  Experiment.  — 
Draw  a  ligature  about  the  ventricle  halfway  be- 
tween base  and  apex  tightly  enough  to  crush  the 
tissues  without  wholly  separating  them.  The 
anatomical  continuity  between  the  two  halves 
of  the  ventricle  will  thereby  be  maintained,  but 
the  physiological  continuity  will  be  lost.  Eelease 
the  ligature. 

The  isolated  "apex"  as  a  rule  does  not  con- 
tract.    The  exceptions  can  probably  be  explained 


532  THE    OUTGO   OF    ENEKGY 

as  the  effect  of  a  constant  stimulus  (see  page 
533). 

The  apical  half  of  the  normal  ventricle  con- 
tains no  nerve  cells.  Consequently  its  failure  to 
contract  after  its  separation  from  the  remainder 
of  the  heart  would  indicate  that  the  adult  heart 
muscle  is  incapable  of  spontaneous  rhythmical 
contraction.  It  has  been  shown,  however,  that  the 
"  apex  "  of  the  mammalian  heart  will  beat  after 
its  complete  removal  from  the  remainder  of  the 
heart,  provided  the  circulation  in  the  extirpated 
piece  is  maintained  by  supplying  it  with  blood. 

Rhythmic  Contractility  of  Heart  Muscle. —  Fur- 
ther evidence  of  the  rhythmic  contractility  of 
the  heart  muscle  is  found  in  the  bulbus  arteriosus. 

Place  very  small  pieces  of  the  bulbus  arteri- 
osus in  normal  saline  solution  under  the 
microscope. 

They  will  contract  rhythmically. 

Histological  examination  shows  that  nerve 
cells  seldom  occur  in  the  bulbus.  It  is  scarcely 
credible  that  they  are  present  in  each  of  the  small 
pieces  seen  contracting  under  the  microscope. 

Constant  Stimulus  may  cause  Periodic  Contrac- 
tion. —  In  a  frog  with  ventricular  apex  isolated 
by  Bernstein's  ligature,  compress  one  or  both 
aortaB,  thus  raising  the  pressure  in  the  ventricle. 


THE    CIRCULATION    OF   THE    BLOOD  533 

The  increased  intracardiac  pressure  acts  as  a 
constant  stimulus  to  the  cardiac  muscle  and  the 
hitherto  inactive  apex  begins  to  contract  again. 

Thus  a  constant  stimulus  may  discharge  peri- 
odic contractions  in  a  muscle  habituated  to 
periodic  contractions  -(compare  page  144)  ;  the 
galvanic  current  and  chemical  stimuli,  such  as 
delphinin,  are  further  examples  of  constant  stim- 
uli which  call  forth  rhythmic  contractions  of  the 
heart  muscle. 

The  Inactive  Heart  Muscle  still  Irritable.  — Stim- 
ulate the  inactive  "  apex  "  mechanically  and  with 
single  induction  shocks. 

The  apex,  though  incapable  of  spontaneous 
rhythmic  contractions,  is  still  irritable,  and  will 
respond  by  a  single  contraction  to  each  stimulus. 

Refractory  Period  :  Extra-Contraction ;  Compen- 
satory Pause.  —  Put  the  electromagnetic  signal 
in  the  primary  circuit.  Connect  the  binding- 
posts  on  the  heart-holder  to  the  secondary  coil  of 
the  inductorium.  Arrange  the  latter  for  single 
induction  currents.  Place  the  ventricle  on  the 
heart-holder.  Send  maximal  make  and  break 
induction  currents  through  the  ventricle  from 
time  to  time  in  each  phase  of  the  cardiac  cycle. 

Note  that  (1)  the  stimulus  sometimes  calls 
forth  an  extra-contraction ;  (2)  at  other  times 
the  stimulus  causes  no  contraction,  having  fallen 


534  THE  OUTGO   OF   ENERGY 

into  the  ventricle  during  the  period  in  which  it 
is  refractory  towards  stimuli ;  (3)  the  extra-con- 
traction is  followed  by  a  pause,  called  the  com- 
pensatory pause  because  it  usually  restores  the 
rate  of  beat  to  that  existing  before  the  extra- 
contraction  took  place. 

Using  induction  currents  of  equal  intensity, 
find  the  limits  of  the  refractory  period  and  note 
them  on  the  drum.  Note  also  the  point  in  the 
cardiac  cycle  at  which  the  maximum  extra- 
contraction  can  be  obtained. 

The  Transmission  of  the  Contraction  Wave  in  the 
Ventricle ;  Engelmann's  Incisions.  —  The  action 
current  of  the  heart  is  taken  to  be  an  expression 
of  the  excitation  process,  although  the  nature  of 
the  latter  is  not  yet  understood.  It  has  already 
been  shown  (page  310)  that  the  action  current 
sweeps  rapidly  over  the  ventricle  preceding  the 
contraction.  The  excitation  might  be  propagated 
by  nerves  or  by  muscle  fibres.  The  following 
experiment  affords  some  evidence  that  the 
transmission  is  by  means  of  muscular  tissue. 

Leaving  the  heart  in  situ,  cut  the  ventricle 
into  a  zigzag  strip  by  obliquely  transverse  in- 
cisions beginning  near  the  apex.  The  nerve 
fibres  in  the  ventricle  will  thereby  be  severed 
at  some  part  or  other  of  their  course,  but  muscular 
continuity  will  be  preserved. 


THE   CIRCULATION   OF   THE    BLOOD  535 

The  contraction  wave  will  pass  over  the  entire 
zigzag  strip.  Normally  the  wave  starts  at  the 
base  and  proceeds  to  the  apex,  but  by  artificial 
stimulation  it  can  be  made  to  pass  from  the 
apex  towards  the  base.  A  similar  result  can  be 
secured  with  the  auricle. 

The  Transmission  of  the  Cardiac  Excitation  from 
Auricle  to  Ventricle  ;  Gaskell's  Block.  —  The  con- 
traction wave  can  be  seen  to  begin  normally  in 
the  sinus  and  thence  to  pass  rapidly  over  the 
auricle ;  on  reaching  the  auriculo-ventricular 
junction  there  is  a  distinct  pause  termed  the 
auriculo-ventricular  interval ;  finally,  the  excita- 
tion reaches  the  ventricle,  and  the  contraction 
wave  is  seen  to  traverse  the  ventricular  muscle 
as  noted  above.  The  auriculo-ventricular  inter- 
val may  be  lengthened  by  any  natural  or  arti- 
ficial hindrance  to  the  passage  of  the  excitation 
wave. 

1.  Place  the  Gaskell  clamp  about  the  auriculo- 
ventricular  junction.  Very  cautiously  turn  the 
screw  until  the  rubber  edge  makes  a  gentle 
pressure  on  the  cardiac  tissues  at  that  point. 

With  careful  work  a  degree  of  pressure  will  be 
reached  that  diminishes  the  conductivity  of  the 
muscle  fibres  joining  the  auricle  and  ventricle  so 
far  as  to  permit  only  every  second  or  every  third 
excitation  to  pass.     The  auricle  will  beat  with- 


536  THE   OUTGO   OF   ENERGY 

out  change  of  frequency,  but  the  ventricle  will 
contract  only  when  the  excitation  succeeds  in 
passing  the  block. 

2.  Divide  the  auricles  in  two  pieces  con- 
nected by  a  small  bridge  of  auricular  tissue. 
Stimulate  one  piece. 

The  stimulation  of  one  piece  will  be  followed 
immediately  by  the  contraction  of  that  piece, 
and,  after  an  interval,  by  the  contraction  of  the 
other.  The  smaller  the  bridge,  the  longer  the 
interval. 

Gaskell  has  pointed  out  that  a  natural  block 
is  furnished  by  the  small  number  of  the  muscle 
fibres  joining  the  auricle  to  the  ventricle,  and 
that  this  natural  block  explains  the  auriculo- 
ventricular  interval,  i.  e.  the  delay  which  the 
excitation  experiences  in  passing  from  the  auricle 
to  the  ventricle. 

3.  Eepeat  Experiment  1,  but  place  the  screw- 
clamp  across  the  middle  of  the  ventricle. 

The  passage  of  the  excitation  from  one  part  of 
the  ventricle  to  another  will  be  delayed  or  inter- 
rupted by  the  lowering  of  the  conductivity  in 
the  compressed  portion. 

Many  irregularities  in  the  frequency  and  force 
of  the  heart  can  be  explained  by  variation  in  the 
conductivity  of  its  several  parts.     They  can  be 


ni>7 


THE   CIRCULATION   OF   THE    BLOOD  537 

explained  also,  by  variations  in  the  irritability  of 
the  several  parts.  In  the  latter  case,  the  excita- 
tion would  pass  as  usual,  but  its  action  on  any 
part,  for  example  the  ventricle,  would  be  in- 
creased or  diminished  by  changes  in  the  irri- 
tability of  the  cardiac  muscle  in  that  region. 
Engelmann  has  found  that  ventricular  systole 
lowers  the  conductivity  of  the  ventricle  for  a 
time. 

Tonus.  —  Pass  the  very  fine  copper  wire  through 
the  wall  of  the  auricle  of  the  tortoise  and  attach 
the  wire  to  the  heart  lever,  so  that  the  contrac- 
tions of  the  auricle  may  be  recorded.  Let  the 
drum  move  so  slowly  that  the  individual  contrac- 
tions will  be  nearly  but  not  quite  fused. 

Two  sorts  of  contractions  can  be  distinguished, 
(1)  the  usual  frequent  contraction  or  beat  of  the 
auricle,  (2)  the  tonus  oscillations.  The  tonus 
oscillations  include  from  twenty  to  forty  beats. 
•In  the  tortoise  auricle,  the  beats  usually  become 
less  extensive  during  the  rise  of  tonus. 

The  Influence  of  "Load"  on  Ventricular  Contrac- 
tion.—  Eecord  the  contractions  of  the  frog's 
ventricle.  Increase  the  intraventricular  pressure 
(i.  e.  the  load  against  which  the  ventricular  muscle 
contracts)   by  clamping  the  aortas  with  forceps 


538  THE   OUTGO   OF  ENERGY 

the  blades  of   which   are    covered  with   rubber 
tubing. 

The  force  of  the  individual  contractions 
will  be  increased  but  their  frequency  will  be 
diminished. 

The  Influence  of  Temperature  on  Frequency  of 
Contraction.  —  Let  the  drum  move  at  such  a 
speed  that  the  individual  heart-beats  in  the 
curve  shall  be  close  together,  but  yet  separate 
and  distinct.  Surround  with  normal  saline  solu- 
tion at  25°  C. 

The  frequency  of  contraction  will  be  increased. 

Keplace  the  warm  solution  with  normal  saline 
solution  at  5°  C. 

The  frequency  of  contraction  will  be  dimin- 
ished. 

The  Action  of  Inorganic  Salts  on  Heart  Muscle. — 
Sever  the  apical  two-thirds  of  the  ventricle  of  the 
tortoise  heart  from  the  remainder  of  the  ventricle 
by  a  cut  parallel  with  the  auriculo-ventricular' 
furrow.  With  a  second  parallel  cut  remove 
from  the  severed  portion  a  ring  two  or  three 
millimetres  wide.  Divide  the  ring  to  form  a 
strip.  Fasten  one  end  of  the  strip  to  the  short 
limb  of  a  glass  rod  bent  at  a  right  angle.  By 
means  of  a  silk  thread  connect  the  other  end  of 
the  strip  to  a  heart  lever  arranged  to  record  the 


THE   CIRCULATION   OF   THE   BLOOD  539 

contractions  of  the  strip  on  a  very  slowly  moving 
drum. 

Sodium.  —  Immerse  the  strip  of  ventricular 
muscle  in  a  beaker  containing  0.7  per  cent  solu- 
tion of  sodium  chloride. 

After  a  latent  period,  which  may  be  protracted, 
but  usually  is  brief,  a  series  of  rhythmic  con- 
tractions will  be  observed.  The  contractions 
soon  reach  a  maximum  and  then  gradually  die 
away.  Sodium,  although  an  important  stimulus 
to  contraction,  cannot  maintain  the  ventricle  in 
continued  activity. 

The  tonus  of  the  heart  muscle  is  diminished 
by  sodium  chloride. 

Calcium.  —  Surround  a  strip  of  contracting 
ventricular  muscle  with  a  solution  of  calcium 
chloride  isotonic  with  0.7  per  cent  sodium  chlo- 
ride solution  (approximately  1.0  per  cent). 

Contractions  will  cease.  Calcium  added  to 
solutions  of  sodium  chloride,  however,  will 
lengthen  the  period  during  which  the  heart 
muscle  contracts  and  will  increase  the  strength 
of  the  individual  contractions.  Strong  solutions 
of  calcium  chloride  greatly  increase  the  tonus. 

Potassium.  —  Surround  a  non-beating  strip  of 
ventricular  muscle  with  a  solution  of  potassium 
chloride  isotonic  with  0.7  per  cent  sodium 
chloride  solution  (approximately  0.9   per  cent). 


540  THE   OUTGO   OF   ENERGY 

Contractions  will  not  be  produced.  If  potas- 
sium be  applied  to  a  contracting  strip,  the  con- 
tractions will  cease. 

Combined  Action  of  Sodium,  Calcium,  and 
Potassium,  —  Surround  the  ventricular  muscle 
with  a  solution  containing  sodium  chloride  (0.7 
per  cent),  calcium  chloride  (0.0026  per  cent), 
and  potassium  chloride  (0.035  per  cent).  This 
is  a  modified  "  Einger  "  solution. 

Long-continued,  rhythmic  contractions  will  be 
secured. 

Observers  are  not  entirely  agreed  as  to  the 
action  of  potassium  and  calcium  on  heart  muscle. 
The  matter  is  of  importance  because  there  is 
much  probability  that  the  rhythmic  contractions 
of  the  heart  are  the  result  of  the  constant  chemi- 
cal stimulus  of  inorganic  salts  present  in  the 
blood.  Most  observers  are  agreed  that  the  inter- 
action of  salts  of  sodium,  calcium,  and  potassium 
is  essential. 

The  fact  that  the  contraction  of  the  heart 
begins  normally  in  the  sinus  may  be  due  to  a 
greater  sensitiveness  of  that  part  to  chemical 
stimulation. 


THE    CIRCULATION    OF    THE    BLOOD  541 


The  Heart  Sounds 

With  a  binaural  stethoscope  auscultate  the 
chest  over  its  entire  extent  during  normal  respi- 
ration and  while   the   subject  holds  his  breath. 

1.  Xote  that  two  sounds  are  heard  in  the 
heart  region. 

2.  Determine  at  what  point  each  of  the  sounds 
is  most  distinct. 

It  will  be  found  that  one,  termed  the  "  first 
sound,"  will  be  most  distinct  where  the  ventricle 
comes  nearest  the  surface,  near  the  apex  of  the 
heart,  in  the  space  between  the  fifth  and  sixth 
ribs,  about  2.5  cm.  below  and  2.5  cm.  within  the 
left  nipple.  Close  inspection  of  this  region  in 
persons  not  too  fat  will  show  that  the  chest  wall 
is  raised  at  each  contraction  of  the  heart.  The 
cardiac  impulse,  as  it  is  called,  may  be  felt  dis- 
tinctly by  one  or  two  fingers  laid  in  the  fifth 
intercostal  space.  It  is  caused  by  the  rapid 
increase  in  the  tension  of  the  ventricle. 

The  "  second  sound  "  will  be  heard  most  dis- 
tinctly immediately  over  the  aortic  arch,  near  the 
junction  of  the  second  right  costal  cartilage  with, 
the  sternum. 

3.  Observe  the  two  sounds  with  relation  to 
their  duration,  pitch,  intensity,  and  quality. 


542  THE    OUTGO   OF    ENERGY 

The  first  sound  in  comparison  with  the  second 
is  of  longer  duration,  lower  pitch,  and  greater 
intensity.  The  quality  of  the  first  sound  is  dull, 
booming  ;  that  of  the  second  is  sharp,  valvular. 

4.  With  one  finger  feeling  the  cardiac  impulse 
observe  the  sounds  with  reference  to  systole  and 
diastole. 

The  first  sound  will  be  found  to  be  systolic, 
i.  e.  it  occurs  with  the  contraction  of  the  ventricle, 
while  the  second  sound  is  diastolic,  being  heard 
at  the  beginning  of  ventricular  relaxation.  The 
interval  between  the  first  and  second  sounds  is 
therefore  very  brief.  The  pause  after  the  second 
sound  before  the  first  is  heard  again,  is  consider- 
ably longer. 

The  first  sound  can  be  heard  in  the  extirpated, 
bloodless  heart  (dog).  The  contraction  of  the 
ventricular  muscle  is  therefore  alone  sufficient 
for  its  production.  But  the  sound  is  modified  or 
replaced  by  a  murmur  when  the  auriculo-ven- 
tricular  valves  are  sufficiently  injured.  It  is 
probable,  therefore,  that  the  sudden  increase  in 
the  tension  of  the  auriculo-ventricular  valves  con- 
tributes to  its  production.  The  second  sound 
obviously  is  due  to  the  sudden  increase  in  the 
tension  of  the  semilunar  valves.  It  is  replaced 
by  a  murmur  when  these  valves  are  rendered 
incompetent. 


THE    CIRCULATION   OF   THE    BLOOD  543 

Ordinarily  the  ratio  between  the  blood-pressure 
in  the  pulmonary  artery  and  right  ventricle  so 
nearly  equals  the  ratio  between  the  blood 
pressure  in  the  aorta  and  left  ventricle  that  the 
semilunar  valves  in  the  pulmonary  artery  and 
aorta  close  together,  or  nearly  together,  and  their 
respective  sounds  are  heard  as  one.  Pathologic- 
ally, for  example  in  distention  of  the  right  heart 
from  prolonged  violent  exercise,  these  relations 
may  be  so  altered  as  to  produce  between  the  two 
sounds  an  interval  perceptible  to  the  ear.  The 
sound  is  then  said  to  be  reduplicated. 

The  Pressure-Pulse 

Frequency.  —  Palpate  the  radial  pulse  by 
laying  on  the  artery  at  the  wrist  the  ball  (not 
the  tip)  of  the  first,  second,  and  third  fingers  of 
the  right  hand.  The  forearm  of  both  subject 
and  observer  should  be  supported  in  a  comfort- 
able position.  Count  the  pulse  in  four  successive 
periods  of  fifteen  seconds.  The  counting  of  the 
observer's  instead  of  the  subject's  pulse  may  be 
avoided  by  noting  whether  the  subject's  supposed 
pulse  is  synchronous  with  the  observer's  heart- 
beat. 

Note  the  frequency  per  minute  when  the  sub- 
ject is  standing,  sitting,  lying,  swallowing,  hold- 
ing the  breath ;   and  before  and  after  exercise ; 


544  THE    OUTGO   OF   ENERGY 

for  example,  before  and  after  lifting  the  weight 
of  the  body  ten  times  by  rising  on  the  toes. 

Sex,  eating,  the  time  of  day,  the  temperature, 
and  many  other  factors  also  influence  the  fre- 
quency of  the  pulse. 

Hardness.  — ■  When  pressure  is  made  upon  an 
artery  in  any  part  of  its  course,  the  pressure  is 
transmitted  in  all  directions  through  the  liquid 
contained  in  the  peri-arterial  tissues,  and  the 
artery  becomes  smaller.  Part  of  the  pressure  is 
used  upon  the  peri-arterial  tissues  themselves. 
When  the  remaining  pressure  equals  the  maxi- 
mum blood-pressure  in  the  artery  at  the  point  of 
compression,  the  blood-pressure  on  the  distal 
side  of  this  point  will  sink  to  the  level  of  the 
blood-pressure  in  the  nearest  .anastomosis.  If 
the  anastomosis  is  of  capillary  size,  the  pulse  will 
disappear.  A  pulse  which  is  obliterated  by  slight 
pressure  is  termed  "  soft ; "  if  the  pressure  re- 
quired is  relatively  considerable,  the  pulse  is 
termed  "  hard."  The  hardness  of  the  pulse  is 
therefore  a  measure  of  the  maximum  blood- 
pressure  at  the  point  of  compression,  less  the 
variable  and  unknown  quantity  required  for  the 
compression  of  the  elastic  tissues. 

Form.  —  1.  The  vibrations  which  follow  the 
primary  pulse  wave  cannot  ordinarily  be  recog- 
nized by  the  palpating  finger.     When,  however, 


THE   CIRCULATION    OF   THE    BLOOD  545 

the  usual  amplitude  of  the  principal  secondary 
vibration  is  much  increased  and  the  interval  be- 
tween the  primary  and  this  secondary  vibration 
is  not  too  brief,  the  pulse  may  be  felt  to  be 
double,  or  "  dicrotic."  For  example,  dicrotism 
can  be  felt  in  some  ca~ses  of  continued  fever. 

2.  A  pulse  which  is  felt  to  reach  its  maximum 
slowly  is  called  a  "  slow  pulse  "  (pulsus  tardus). 
One  which  reaches  its  maximum  rapidly,  giving 
the  palpating  finger  the  sensation  of  a  quick 
push,  is  said  to  be  a  "  quick  pulse  "  (pulsus  celer). 
Quick  and  slow  pulses  should  be  carefully  dis- 
tinguished from  frequent  and  infrequent  pulses. 

Volume.  —  The  extent  to  which  the  arterial 
wall  is  driven  from  its  position  of  equilibrium 
(volume  or  size  of  pulse)  is  a  function  of  the 
output  of  the  ventricle,  the  outflow  period, 
the  peripheral  resistance,  and  the  elasticity  of 
the  arteries.  It  is  measured  very  inexactly  by 
the  palpating  finger  and  the  sphygmograph,  accu- 
rately by  the  plethysmograph  (page  552). 

The  Pressure-Pulse  in  the  Artificial  Scheme.  — 
Eevolve  the  disk  of  the  artificial  scheme  until 
the  arterial  pressure  is  maintained  at  50  mm. 
Hg.  Close  the  tube  leading  to  the  arterial 
manometer,  so  that  the  oscillations  of  the 
mercury  may  not  influence  the  curves  to  be 
taken.     Attach   the   small  thistle-tube  (without 

35 


546  THE   OUTGO    OF    ENERGY 

rubber  membrane)  to  the  sphygmograph  (Fig. 
70)  and  adjust  the  tube  upon  the  aorta.  Close 
the  side  branch  of  the  sphygmograph  tube.  Bring 
the  writing  point  of  the  sphygmograph  lever 
against  a  slow-moving,  lightly-smoked  drum. 
Kecord  a  series  of  pulse  curves. 

Note  the  quick  upstroke,  corresponding  to  the 
quick  distention  of  the  artery  by  the  emptying 
of  the  ventricle,  and  the  gradual  downstroke, 
corresponding  to  the  gradual  emptying  of  the 
artery  through  the  resistance  during  the  diastole 
or  interval  between  two  beats.  Near  the  apex 
of  the  more  delicately  written  curves  may  be 
seen  a  slight  depression,  the  dicrotic  notch. 

It  is  obvious  that  the  changes  observed  in  the 
size  of  the  artery  are  the  expression  of  changes 
in  the  blood-pressure.  The  pulse  is  a  function 
of  the  blood-pressure  at  the  point  observed. 
Hence  the  term  pressure-pulse. 

The  Human  Pressure-Pulse  Curve.  —  1.  Adjust 
the  lever  of  the  recording  tambour  so  that  it  shall 
write  with  the  least  friction  possible  on  a  thinly 
smoked  drum.  Let  the  drum  revolve  slowly 
(two  revolutions  a  minute).  Be  sure  that  the 
side  branch  is  open.  Place  the  larger  thistle- 
tube,  which  serves  as  a  "  receiving  tambour,'* 
over  the  carotid  artery,  anterior  to  the  stern o- 
cleidomastoideus  muscle,  about  the  level  of  the 


THE   CIRCULATION   OF  THE   BLOOD  547 

thyroid  cartilage.  When  the  tambour  (without 
rubber  membrane)  is  pressed  well  down  over  the 
artery,  let  an  assistant  close  the  side  branch.  If 
the  receiving  tambour  has  been  properly  placed, 
the  recording  tambour  will  write  a  sharply 
marked  pulse  curve.  If  none  such  appears,  open 
the  side  branch  and  move  the  receiving  tambour 
into  a  better  position. 

Indicate  the  primary  wave,  the  predicrotic 
elevation,  and  the  dicrotic  notch. 

2.  Cover  the  thistle-tube  with  a  rubber  mem- 
brane. Cement  in  the  centre  of  the  membrane  a 
bone  collar-button.  Place  the  button  upon  the 
radial  artery  at  the  wrist  and  record  the  radial 
pulse. 

It  will  be  found  that  the  degree  of  pressure 
must  be  carefully  regulated  in  order  to  secure  a 
satisfactory  curve.  The  blood-pressure  in  the 
artery  normally  is  held  in  equilibrium  by  the 
elastic  tension  of  the  wall  of  the  artery  and  the 
surrounding  tissues.  The  pressure  of  the  sphyg- 
mograph  increases  the  tension  of  the  peri-arterial 
tissues  and  thus  assists  in  holding  the  blood- 
pressure  in  equilibrium.  The  greater  the  pres- 
sure of  the  sphygmograph,  the  larger  the  part  of 
the  blood-pressure  borne  by  it  and  the  more  com- 
pletely will  variations  in  the  blood-pressure  be 
made   visible   in   the  pulse  curve.     The  record, 


548  THE    OUTGO    OF   ENERGY 

however,  is  not  a  measure  of  the  absolute  blood- 
pressure,  because  it  is  not  possible  io  estimate 
accurately  how  much  of  the  blood-pressure  is 
still  held  in  equilibrium  by  the  elastic  tension 
of  the  arterial  wall  and  the  surrounding  tissues. 
The  pulse  curve  does  give  with  approximate 
correctness  the  variations  in  the  blood-pressure. 
The  correctness  would  be  complete  were  it  not 
that  the  part  of  the  blood-pressure  held  in 
equilibrium  by  the  elastic  tension  of  the  arterial 
wall  varies  with  the  size  of  the  vessel,  and  the 
size  of  the  vessel  increases  as  the  blood-pressure 
increases.  Thus  the  portion  of  the  blood-pres- 
sure which  fails  of  record  constantly  varies. 
The  error  thus  introduced  is  not  important. 
The  sphygmograph,  therefore,  gives  a  practically 
true  record  of  the  form  of  the  pulse,  i.  e.  the 
time-relations  of  the  changes  in  blood-pressure. 
This  knowledge  cannot  possibly  be  secured  by 
the  palpation  of  the  pulse.  The  sphygmograph, 
it  may  be  repeated,  does  not  give  a  true  record 
of  the  absolute  blood-pressure  (hardness)  or  of 
the  amplitude  (size)  of  the  pulse.  Both  hardness 
and  amplitude  are  better  measured  by  the  pal- 
pating finger. 

In  many  sphygmographs,  for  example,  Marey's 
and  Dudgeon's,  the  pressure  on  the  artery  is 
made  by  a  metal  spring,  the  movements  of  which 


THE   CIRCULATION    OF   THE   BLOOD  540 

are  recorded  by  a  lever.  In  the  record  just  taken 
from  the  radial  artery,  the  pressure  was  made  by 
the  elastic  tension  of  the  rubber  membrane  clos- 
ing the  thistle-tube.  In  the  case  of  the  carotid 
artery,  this  membrane  is  replaced  by  the  skin  of 
the  neck. 

In  every  instance,  the  sphygmograph  records 
the  changes  of  blood-pressure  in  a  section  of  the 
artery  so  short  in  comparison  with  the  length  of 
the  whole  arterial  tree  as  to  be  practically  a 
cross-section. 

Low  Tension  Pressure-Pulse.  —  1.  In  the  arti- 
ficial scheme  open  slightly  the  side-branch  that 
permits  the  liquid  in  the  arterial  tubes  to  flow 
out  without  passing  through  the  resistance.  The 
arterial  pressure  will  fall  in  consequence  of  the 
diminished  peripheral  resistance.  Normally  this 
effect  is  produced  by  a  dilatation  of  the  smaller 
arteries.  Let  the  arterial  pressure  fall  to  about 
20  mm.  Hg.     Eecord  a  series  of  pulse  curves. 

Note  that  the  oscillations  of  the  mercury 
column  with  each  ventricular  beat  are  much 
higher  than  with  normal  pressure  (120-150  mm.). 
Feel  the  pulse  with  the  finger.  With  each  beat 
the  artery  quickly  expands  and  as  quickly  re- 
laxes.    The  artery  is  "softer"  than  usual. 

2.  Feel  the  normal  pulse  in  the  radial  artery. 
Note    the  normal  "  hardness."     Let  the   subject 


550  THE   OUTGO   OF   ENERGY 

inhale  two  drops  (on  no  account  more  than  two) 
of  the  nitrite  of  amyl  (to  be  dropped  on  a  hand- 
kerchief by  one  of  the  instructors).  This  power- 
ful drug  causes  dilatation  of  the  blood  vessels, 
particularly  the  smaller  arteries. 

Observe  that  as  the  face  flushes,  indicating  the 
vascular  dilatation,  the  pulse  will  be  softer. 

Do  not  repeat  the  experiment. 

Pressure-Pulse  in  Aortic  Regurgitation. — Empty 
the  principal  tubes  of  the  artificial  scheme.  Re- 
move the  rubber  from  about  the  aortic  valve. 
Replace  the  valve  tube.  Till  the  apparatus  with 
water.  Revolve  the  disk  at  the  rate  and  with 
the  force  employed  to  imitate  the  normal  circula- 
tion (page  545). 

Feel  the  pulse  with  the  finger. 

After  each  systole  the  liquid  streams  back 
through  the  incompetent  valve.  The  ventricle 
is  thus  fuller  than  normal  at  the  beginning  of 
the  stroke,  while  the  arteries  are  less  than 
normally  full.  Consequently  more  than  the 
usual  quantity  is  discharged  by  the  ventricle 
into  relatively  undistended  arteries.  The  rela- 
tively lax  artery  is  thereby  quickly  and  largely 
expanded,  as  indicated  by  the  quick  thrust  given 
the  palpating  finger  and  by  the  large  excursion 
of  the  mercury  in  the  arterial  manometer. 

Record  pulse  curves. 


THE    CIRCULATION   OF   THE    BLOOD  551 

The  upstroke  is  unusually  high  and  quick.  It 
is  at  once  followed  by  a  great  and  sudden  fall. 
Obviously  a  relatively  empty  artery  has  been 
suddenly  filled  by  an  unusually  large  inflow  and 
has  been  suddenly  emptied  again  through  the 
broken  valve  and  the  capillaries.  The  pulse- 
curve  shows  low  arterial  tension,  but  is  of  greater 
amplitude  than  the  pulse  in  which  low  tension 
results  from  lowering  the  peripheral  resistance. 
In  the  body,  the  amplitude  of  the  pulse  in  aortic 
regurgitation  is  increased  by  the  greater  force 
with  which  the  ventricle  contracts,  as  well  as  by 
the  larger  quantity  discharged  at  each  beat,  for 
the  back-flow  from  the  aorta  dilates  the  ventricle 
and  usually  causes  the  walls  of  the  ventricle  to 
increase  in  thickness  (dilatation  with  hypertrophy 
of  the  ventricle). 

Stenosis  of  the  Aortic  Valve.  —  Eeplace  the  rub- 
ber flap  upon  the  aortic  valve-tube,  and  tie  a 
string  around  the  flap  and  tube  just  over  the 
opening  in  the  tube.  Stenosis,  i.  e.  narrowing,  of 
the  opening  will  thus  be  secured.  Put  the  valve- 
tube  in  place,  and  compress  the  bulb  at  the  usual 
rate.     Eecord  pulse  curves. 

The  slow  difficult  emptying  of  the  ventricle 
will  be  evident  in  the  curve  and  to  the  hand. 
The  movements  of  the  arterial  manometer  are 
sluggish    and    of    diminished    amplitude.      The 


552  THE    OUTGO    OF   ENERGY 

pulse  wave  is  small  and  the  upstroke  slow, 
corresponding  to  the  small  slow  inflow  through 
the  stenosed  valve. 

Eestore  the  valve  to  its  normal  state. 

Incompetence  of  the  Mitral  Valve.  —  Remove 
the  rubber  flap  from  the  mitral  valve.  Record 
pulse  curves  as  before. 

The  pulse  will  be  small,  because  the  pressure 
in  the  auricle  (in  this  case  the  reservoir  of  water) 
is  always  low,  while  the  pressure  in  the  arteries 
is  always  high.  Hence  the  ventricle  will  partly 
empty  itself  through  the  incompetent  mitral 
valve,  in  the  direction  of  low  resistance,  before 
the  pressure  in  the  ventricle  rises  high  enough  to 
open  the  aortic  valve  against  the  high  aortic 
pressure.  The  quantity  remaining  in  the  ventri- 
cle when  the  intraventricular  pressure  rises  high 
enough  to  open  the  aortic  valve  is  not  sufficient 
to  distend  the  arteries  to  the  normal  degree. 

In  mitral  stenosis  the  pulse  is  also  small 
because  the  narrowing  of  the  mitral  orifice  per- 
mits less  than  the  usual  quantity  of  liquid  to 
enter  the  ventricle. 

The  Volume  Pulse 

Remove  the  receiving  tambour  of  the  sphygmo- 
graph  from  its  tube,  and  insert  the  plethysmo- 
graph    cylinder   (this   is   the   tube  used   in    the 


THE    CIRCULATION    OF    THE    BLOOD  553 

experiment  on  the  volume  of  contracting  muscle, 
Fig.  58).  Place  the  middle  finger  in  the  cylinder, 
making  sure  that  the  rubber  collar  fits  around 
the  finger  tightly,  but  without  impeding  the 
venous  circulation.     Close  the  side  branch. 

Periodical  alterations  in  the  volume  of  the 
finger  will  be  recorded  ;  they  have  the  rhythm  of 
the  heart-beat.  (The  friction  of  the  writing-lever 
must  be  very  slight  to  insure  success,  and  the 
curve  at  best  will  be  small.) 

Determine  the  effect  of  straining  and  forced 
respiration  upon  the  curve. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Artificial 
scheme.  Microscope.  Mesentery  board.  Mercury  man- 
ometer. Aortic  cannula.  One  per  cent  solution  of  sodic 
carbonate.  Ligature.  Glass  rod  one  inch  long.  Frog- 
board.  Wooden  stand.  Kymograph.  Inductorium.  Dry 
cell.  Electrodes.  Key.  Electromagnetic  signal.  Sphyg- 
mograph  with  large  anu  small  thistle-tubes.  Rubber 
membrane.  Bone  collar-button.  Heart-holder.  Screw- 
clamp.  Muscle  lever  with  scale-pan  and  weights.  Stand. 
Fine  copper  wire.  Tortoise  with  heart  exposed.  Ice. 
Solution  of  sodium  chloride,  0.7  per  cent.  Solutions  of 
calcium  chloride,  and  potassium  chloride,  each  isotonic 
with  0.7  per  cent  solution  of  sodium  chloride.  A  solu- 
tion containing  sodium  chloride,  0.7  per  cent ;  calcium 
chloride,  0.026  per  cent;  and  potassium  chloride,  0.035 
per  cent.  Binaural  stethoscope.  Nitrite  of  amyl.  Ple- 
thysmograph. 


554  THE    OUTGO    OF   ENERGY 


XIII 

THE  INNERVATION  OF  THE  HEART  AND 
BLOOD-VESSELS 

The  quantity  of  blood  required  by  the  tissues 
varies  from  time  to  time.  For  example,  the 
digestive  organs  require  more  blood  when  food 
is  taken  than  at  other  times.  Variations  in  the 
blood  supply  of  the  individual  organs  are  accom- 
plished chiefly  by  varying  the  size  of  their  blood 
vessels.  To  this  end  the  blood  vessels  are  pro- 
vided with  muscular  coats  which  are  made  to 
contract  or  relax,  and  thus  to  constrict  or  dilate 
the  vessels.  The  impulse  to  contraction  or  relax- 
ation is  given  by  the  vasomotor  nerves.  It  is 
necessary,  too,  that  the  force  and  frequency  of 
ventricular  contraction  should  vary  with  the 
resistance  to  be  overcome,  the  need  for  more 
rapid  oxygenation  of  the  blood,  etc.,  and  special 
nerves  are  provided  for  this  purpose  also.  The 
control  or  innervation  of  the  heart  and  blood 
vessels  will  now  be  considered. 

The  heart  is  provided  with  nerves  that  aug- 
ment and  nerves  that  inhibit  its  action. 


innervation  of  heart  and  blood-vessels    555 

The  Augmentor  Nerves  of  the  Heart 

In  the  frog  both  the  augmentor  and  the  inhibi- 
tory nerves  reach  the  heart  through  the  splanch- 
nic branch  of  the  vagus.  The  augmentor  fibres 
leave  the  spinal  cord  in  the  third  spinal  nerve,  and 
pass  through  the  ramus  communicans  of  this 
nerve  into  the  third  sympathetic  ganglion,  where 
they  probably  end  in  contact  with  the  body  or 
processes  of  sympathetic  cells.  The  axis-cylin- 
ders of  these  sympathetic  cells  pass  up  the  cer- 
vical sympathetic  chain  to  the  ganglion  of  the 
vagus  (Fig.  72),  and  thence  down  the  vagus  trunk 
to  the  heart.  Thus  in  the  greater  part  of  its 
course  the  vagus  cannot  be  stimulated  without 
exciting  both  the  augmentor  and  the  inhibitory 
cardiac  fibres.  To  excite  either  alone  it  is  neces- 
sary to  stimulate  the  respective  nerves  above 
their  junction. 

Preparation  of  the  Sympathetic.  —  Cut  away  the 
lower  jaw  of  a  large  frog,  the  brain  of  which  has 
been  destroyed  by  pithing,  and  continue  the  slit 
from  the  an^le  of  the  mouth  downwards  for  a 
short  distance.  Avoid  cutting  the  vagus  nerve 
(Fig.  73).  Turn  the  parts  well  aside,  and  expose 
the  vertebral  column  where  it  joins  the  skull. 
Eemove  the  mucous  membrane  covering  the 
roof  of  the  mouth.     The  sympathetic  is  situated 


556 


THE    OUTGO   OF   ENEEGY 


immediately  under  the  levator  anguli  scapulse 
muscle,  which  must  be  carefully  removed.  The 
nerve  will  then  be  visible.  It  is  commonly  pig- 
mented and  usually  lies  under  an  artery.  Care- 
fully isolate  the  nerve.     Put  a  ligature  around  it 


LAS 


.*V\  :> *■ 


LAS 


i  r> «. 


LjAo 


Fig.  72.  Scheme  of  the  sympathetic  nerve  in  the  frog.  OC.  Occiput. 
LAS.  Levator  anguli  scapulse.  Sym.  Sympathetic.  GP.  Glosso-pharyn- 
geus.  V-S.  Vago-sym pathetic.  G.  Ganglion  of  the  vagus.  Ao.  Aorta. 
HA.  Subclavian  artery.  (After  Stirling's  reproduction  of  Gaskell  and 
Gadow's  plate.) 


as  far  away   from  the  skull  as  practical >le,  and 
cut  the  nerve  caudal  to  the  ligature. 

Action  of  the  Sympathetic  on  the  Heart.  — 
Arrange  the  inductorium  for  weak  tetanizing  cur- 
rents.    In  the  primary  circuit  place  the  electro- 


INNERVATION    OF    HEART    AND    BLOOD-VESSELS     557 

magnetic  signal.  Prepare  the  sympathetic  as 
directed  above.  Expose  the  heart  (page  75). 
Place  it  in  the  heart-holder.  Should  the  heart 
beat  rapidly,  slow  it  with  ice.  Let  the  writing 
point  record  above  the  point  of  the  electromag- 
netic signal  on  a  drum  revolving  so  slowly  that 
the  individual  beats  shall  appear  in  the  curve 
very  close  together,  yet  far  enough  apart  to  be 
readily  counted.  Divide  the  observation  into 
nine  periods  of  twenty  seconds  each.  Place  the 
electrodes  beneath  the  sympathetic,  with  the 
short-circuiting  key  closed.  Adjust  the  heart 
lever  to  write  its  curve.  Let  the  assistant  call 
the  beginning  of  each  period  as  he  marks  it  on 
the  drum.  At  the  beginning  of  the  second  pe- 
riod, open  the  short-circuiting  key ;  at  the  begin- 
ning of  the  third  period,  close  the  short-circuiting 
key.  Lower  the  drum  when  one  circuit  is 
completed. 

Count  the  number  of  beats  in  each  period.  The 
frequency  will  be  increased.  The  force  of  con- 
traction will  also  be  increased.1  The  latent  period 
of  excitation  is  long  and  there  is  a  prolonged 
after-effect.  The  former  frequency  is  regained 
more  rapidly  after  short  than  after  long  stimula- 
tions.    The  speed  of  the  cardiac  excitation  wave 

1  The  stimulation  of  the  augmentor  fibres  is  difficult  and 
often  fails  in  winter  frogs. 


558 


THE    OUTGO   OF    ENERGY 


(compare  page  336)  is  increased  and  the  time  of 
its  passage  across  the  auriculo-ventricular  groove 
is  shortened,  though  this  cannot  be  observed  by 
the  method  used  in  the  present  experiment. 

The  Inhibitory  Nerves  of  the  Heart 

The   Preparation   of  the  Vagus  Nerve.  —  Fasten 
a  lame  fros?  on  the  board,  back  down.     Pass  the 


Fig.  73.  Scheme  of  the  cervical  nerves  in  the  frog  (after  Schenck). 
G.  P.  Glosso-pharyngeus.  Hg.  Hypoglossus.  V.  Vagus.  L.  Laryngeus. 
K.  Posterior  end  of  lower  jaw.  The  glosso-pharyngeus  has  been  drawn 
to  one  side  of  the  hypoglossus  for  the  sake  of  clearness. 

glass  tube  through  the  oesophagus  into  the 
stomach.  Eemove  the  muscles  lying  over  the 
petrohyoid  muscle,  which  passes  from  the  base  of 
the  skull  to  the  horn  of  the  hyoid  bone.     Lying 


INNERVATION    OF    HEART    AND    BLOOD-VESSELS     559 

near  the  line  between  the  angle  of  the  jaw  and 
the  auricle  are  four  nerves  (Fig.  73)  :  (1)  The 
hypoglossals.  This  nerve  is  superficial.  Near 
their  emergence  from  the  skull  it  is  the  lowest 
of  the  nerves,  but  later,  the  uppermost.  It  crosses 
the  remaining  nerves  and  the  blood-vessels,  and 
passes  forwards  and  inwards  towards  the  tongue. 
(2)  The  glosso-pharyngeus,  which  soon  turns  for- 
wards beneath  the  hypoglossus  parallel  to  the 
ramus  of  the  jaw.  (3)  The  vagus,  and  (4)  the 
laryngeus,  the  two  lying  almost  parallel  in  the  line 
between  the  angle  of  the  jaw  and  the  auricle. 
The  laryngeus  rests  on  the  petrohyoid  muscle,  and 
passes  upwards  and  inwards  beneath  the  arteries 
towards  the  larynx.  The  vagus  runs  at  first 
along  the  superior  vena  cava  to  the  auricle ;  a 
branch  is  given  off  to  the  lungs.  Clear  the  vagus, 
tie  a  silk  thread  around  the  nerve  and  sever  the 
nerve  on  the  cranial  side  of  the  ligature,  so  that 
the  peripheral  stump  can  be  placed  on  the  elec- 
trodes for  stimulation.  Divide  the  laryngeal 
branch.  Keep  the  preparation  moist  with  nor- 
mal saline  solution. 

Stimulation  of  Cardiac  Inhibitory  Fibres  in 
Vagus  Trunk.  —  Arrange  the  inductorium  for 
weak  tetanizing  currents.  In  the  primary  circuit 
place  the  electro-magnetic  signal.  Expose  the 
heart.     Place  it   in   the   heart-holder.     Let   the 


560  THE    OUTGO   OF   ENERGY 

writing  point  record  exactly  above  the  point  of 
the  electromagnetic  signal  on  a  drum  revolving  so 
slowly  that  the  individual  beats  shall  appear  in 
the  curve  very  close  together  and  yet  far  enough 
apart  to  be  readily  counted. 

Lay  the  vagus  nerve  on  the  electrodes.  Start 
the  drum.  As  soon  as  good  curves  are  writing, 
start  the  inductorium,  and  open  the  short-circuit- 
ing key  for  about  twenty  seconds.  The  heart  will 
be  inhibited.  Note  that  the  arrested  heart  is  al- 
ways relaxed,  i.  e.  in  diastole.  The  latent  period 
is  short  (one  or  two  heart-beats).  A  brief  after- 
effect is  present.  If  the  stimulus  is  continued, 
the  heart  will  begin  to  beat  even  during  the 
stimulation,  showing  that  the  inhibitory  mechan- 
ism can  be  exhausted.  The  heart  beats  more 
rapidly,  and  usually  more  strongly,  immediately 
after  inhibition  than  before ;  this  probably  is  due 
to  the  after-effect  of  the  stimulation  of  augmentor 
fibres  in  the  vagus  trunk,  as  explained  below. 

Eepeat  the  stimulation,  but  weaken  the  stimu- 
lating current  by  moving  the  secondary  farther 
from  the  primary  coil. 

With  a  suitable  strength  of  current,  the  heart 
will  be  slowed  but  not  arrested.  The  duration 
of  diastole  will  be  markedly  less,  while  the  dura- 
tion of  systole  will  be  changed  but  little  if  at 
all.     A  stronger  excitation  would  lengthen  both 


INNERVATION    OF   HEART   AND    BLOOD-VESSELS     561 

systole  and  diastole.  The  diminution  in  force  often 
appears  before  the  diminution  in  frequency. 

Effect  of  Vagus  Stimulation  on  the  Auriculo-Ven- 
tricular  Contraction  Interval.  —  Counterpoise  two 
inverted  muscle  levers.  Place  their  writing  points 
exactly  above  the  writing  point  of  the  electro- 
magnetic signal.  Pass  fine  bent  pins  through 
the  auricle  and  ventricle,  respectively,  and  con- 
nect them  by  silk  threads  with  the  muscle  levers 
("Suspension  method").  Let  the  drum  revolve 
at  its  fastest  speed.  When  good  auricular  and 
ventricular  contractions  are  obtained,  stimulate  the 
vagus  trunk  with  a  current  not  quite  sufficient  to 
cause  arrest. 

Note  that  the  inhibition  affects  both  the  auricle 
and  the  ventricle.  Weak  stimuli  affect  primarily 
the  auricles.  The  auriculo-ventricular  contrac- 
tion interval  is  lengthened. 

Irritability  of  the  Inhibited  Heart.  —  Arrest  the 
heart  by  stimulating  the  vagus  trunk.  When 
complete  inhibition  is  secured,  touch  the  ventricle 
smartly  with  the  point  of  the  seeker. 

The  ventricle  will  respond  by  a  single  contrac- 
tion. 

When  the  inhibition  is  profound,  the  irritabil- 
ity may  be  so  far  reduced  that  the  heart  will  not 
contract  on  direct  stimulation. 

In  addition  to  the  effects  already  enumerated, 

36 


562  THE    OUTGO   OF   ENERGY 

appropriate  methods  of  observation  would  show 
that  vagus  excitation  increases  the  intraventricu- 
lar pressure  during  diastole,  lessens  the  intake 
and  the  output  of  the  ventricle,  and  diminishes 
the  tonus  of  the  heart  muscle.  The  action  of  the 
vagus  is  accompanied  by  a  positive  electrical 
variation.  The  action  on  the  sinus  and  on  the 
bulbus  does  not  differ  essentially  from  that  upon 
the  ventricle. 

It  has  already  been  pointed  out  that  the  vagus 
of  the  frog  contains  both  inhibitory  and  augment- 
ing fibres.  The  stimulation  of  the  mixed  nerve 
usually  causes  inhibition,  as  described  above,  but 
sometimes  augmentation.  The  augmentation  ob- 
served after  cessation  of  the  inhibitory  effect  is 
probably  explained  by  the  longer  after-effect  of 
the  augmentor  excitation. 

Intracardiac  Inhibitory  Mechanism.  —  Arrange 
an  inductorium  for  tetanizing  currents.  Close 
the  short-circuiting  key.  Expose  a  frog's  heart. 
Eaise  the  heart  with  a  glass  rod.  Note  the  white 
"  crescent "  between  the  sinus  venosus  and  the 
right  auricle.  Set  the  inductorium  in  action. 
Put  the  points  of  the  electrodes  on  the  crescent, 
and  open  the  short-circuiting  key  for  a  moment. 
After  one  or  two  beats  the  heart  will  stop. 

Inhibition  by  Stannius  Ligature.  —  Turn  up  the 
heart  to  expose  its  posterior  surface,  and  note  the 


INNERVATION   OF   HEART    AND    BLOOD-VESSELS     563 

line  of  junction  of  the  sinus  venosus  and  right 
auricle.  Tie  a  ligature  around  the  heart  exactly 
at  this  line,  passing  the  thread  beneath  the  aortas, 
so  that  they  shall  not  be  included  in  the  ligature. 

The  auricles  and  ventricle  cease  to  beat,  for  a 
time  at  least,  while  the  sinus  venosus  continues 
with  unaltered  rhythm.  (The  result  is  usually 
ascribed  to  inhibition,  from  the  mechanical  stim- 
ulation of  the  intracardiac  inhibitory  mechanism. 
If  the  ventricle  begins  spontaneously  to  beat,  as 
may  happen  if  the  ligature  is  not  accurately 
placed,  tie  a  second  ligature  around  the  junction 
of  sinus  and  auricle.) 

Action  of  Nicotine.  —  Apply  nicotine  solution 
(0.2  per  cent)  to  the  ventricle.  After  a  few 
minutes,  stimulate  the  trunk  of  the  vagus  nerve. 
No  curve  need  be  written. 

The  heart  is  not  inhibited. 

Now  lift  the  heart  with  a  glass  rod,  and  stimu- 
late the  intracardiac  inhibitory  nerves. 

The  heart  is  inhibited.  Nicotine  paralyzes 
some  inhibitory  mechanism  between  the  vagus 
and  the  intracardiac  inhibitory  nerves.  But  it  is 
known  that  nicotine  does  not  paralyze  nerve 
trunks.  Hence  it  is  probable  that  the  cardiac 
inhibitory  fibres  do  not  pass  to  the  cardiac  muscle 
directly,  but  end  in  contact  with  nerve  cells, 
which    take    up    the   impulse    and   transmit   it 


564  THE   OUTGO    OF   ENERGY 

through  their  processes  to  the  muscular  fibres  of 
the  heart. 

Atropine.  —  With  a  clean  pipette  apply  a  few 
drops  of  a  solution  of  atropine  (0.5  per  cent)  to 
the  heart.  After  a  few  moments  lift  the  ventri- 
cle and  stimulate  the  crescent. 

The  heart  is  not  inhibited.  Atropine  paralyzes 
the  intracardiac  inhibitory  nerves. 

Muscarine.  —  With  a  fine  pipette  put  upon  the 
ventricle  a  few  drops  of  normal  salt  solution  con- 
taining a  trace  of  muscarine  (a  poisonous  alkaloid 
extracted  from  certain  mushrooms). 

The  ventricle  will  gradually  be  arrested  in 
diastole,  much  distended  with  blood. 

Antagonistic  Action  of  Muscarine  and  Atropine. 
—  With  a  fresh  pipette  apply  a  little  normal  salt 
solution  of  atropine  (0.5  per  cent). 

The  heart  will  commence  to  beat  again. 

The  Centres  of  the  Heart  Nerves 

It  has  been  shown  that  the  heart  receives  in- 
hibitory and  augmenting  nerve  fibres.  The  sit- 
uation of  the  inhibitory  and  augmenting  "  centres," 
i.  e.,  the  nerve  cells  from  which  the  inhibitory 
and  augmenting  fibres  spring,  should  now  be 
considered. 

Inhibitory  Centre.  —  Place  a  frog  and  a  small 
sponge  wet  with  ether  under  a  glass  jar.    Be  very 


INNERVATION   OF    HEART   AND   BLOOD-VESSELS     565 


careful  not  to  kill  the  frog  by  an  overdose  of 
ether.  When  insensibility  is  complete,  place  the 
animal,  back  uppermost,  on 


a  frog-board. 


Cut  through 


the  skin  in  the  median  line 
from  the  nose  about  half 
way  to  the  urostyle.  Care- 
fully uncover  the  roof  of  the 
skull.  Eemove  the  longitu- 
dinal muscles  on  either  side 
of  the  1st,  2d,  and  3d  verte- 
bras. Strip  off  the  parietal 
bones  with  forceps,  begin- 
ning at  the  anterior  end, 
opposite  the  anterior  margin 
of  the  orbit.  Clear  away 
the  occipital  bones.  Saw 
through  the  laminae  of  the 
first  three  vertebrae,  and  re- 
move the  laminae  to  expose 
the  spinal  cord.    Expose  the 


Fig.  74.     View  of  the  brain 
of   a   frog   from    above,  en- 
larged.  L.ol.  Olfactory  lobes, 
heart    by    Cutting    away    the      H.c.    Cerebral    hemispheres. 

G.p.       Pineal    body.      Th.o. 


chest  wall  over  the  pericar- 
dium. Hold  the  frog  in  such 
a  way  that  the  heart  can  be 
observed  while  the  brain  and 
cord  are  stimulated.  With 
needle  electrodes,  the  points  of  which  should  be 


Optic  thalami.  L.op.  Optic 
lobes.  C  Cerebellum.  M.o. 
Medulla  oblongata.  S.rh. 
Sinus  rhomboidalis.  (After 
Foster's  plate  in  Bunion- 
Sanderson's  Handbook.) 


566  THE   OUTGO   OF   ENERGY 

one  millimetre  apart,  stimulate  the  spinal  cord 
with  a  tetanizing  current  of  a  strength  easily 
borne  on  the  tongue. 

Stimulation  of  the  spinal  cord  will  not  inhibit 
the  heart.  Stimulation  of  the  cerebral  hemi- 
spheres will  be  also  ineffectual.  Now  stimulate 
the  medulla  oblongata.     (Fig.  74.) 

The  heart  will  be  inhibited. 

This  method  of  locating  the  cardio -inhibitory 
centre  is  unsatisfactory,  because  the  inhibition 
produced  may  possibly  be  the  result  of  the  stimu- 
lation of  nerve  paths  to  or  from  the  centre.  Its 
results  can  be  controlled  by  the  method  of  suc- 
cessive sections,  to  be  explained  in  connection 
with  the  vasomotor  centre,  page  565. 

The  cardio-inhibitory  centre  is  always  in  ac- 
tion, for  section  of  the  vagi  causes  the  heart  to 
beat  more  frequently. 

Augmentor  Centre.  —  It  is  probable  that  this 
centre,  like  the  inhibitory  centre,  is  situated  in 
the  bulb,  but  the  location  is  not  definitely  known. 
The  constant  activity  of  the  augmentor  centre  is 
shown  by  the  fall  in  frequency  of  beat  after  sec- 
tion of  the  vagi  followed  by  bilateral  extirpation 
of  the  inferior  cervical  and  first  thoracic  ganglia 
in  mammals. 

The  neuraxons,  or  axis-cylinder  processes,  of 
the  augmentor  cells  lying  in  the  central  nervous 


INNERVATION   OF   HEART   AND   BLOOD-VESSELS     567 

system  pass  out  of  the  spinal  cord  in  the  white 
rami  and  terminate  in  the  sympathetic  ganglia 
(for  example,  the  inferior  cervical  and  stellate 
ganglia  of  the  dog)  in  contact  with  sympathetic 
cells,  the  neuraxons  of  which  convey  the  impulse 
to  the  heart. 

The  cardiac  centres  are  readily  affected  by 
afferent  impulses  from  many  sources. 

Reflex  Inhibition  of  the  Heart;  Goltz's  Experi- 
ment. —  In  a  very  lightly  etherized  frog,  expose 
the  pericardium  by  cutting  away  the  chest  wall 
over  the  heart.  Count  the  number  of  beats  in 
periods  of  twenty  seconds.  Continue  the  count 
while  an  assistant  strikes  gentle  blows  with  the 
handle  of  a  scalpel  upon  the  abdomen  at  the  rate 
of  about  140  per  minute. 

The  frequency  will  usually  diminish  and,  in  fa- 
vorable cases,  the  heart  will  at  length  be  arrested. 

Cut  both  vagus  nerves  and  repeat  the  experi- 
ment. 

The  reflex  inhibition  of  the  heart  cannot  be 
obtained  after  section  of  the  vagi. 

It  has  been  shown  by  Bernstein  that  the  affer- 
ent nerves  in  this  experiment  are  abdominal 
branches  of  the  sympathetic  nerve.  The  stim- 
ulation of  the  central  end  of  the  abdominal 
sympathetic  in  the  rabbit  also  produces  reflex 
inhibition  of  the  heart. 


568  THE    OUTGO   OF   ENERGY 

Reflex  Augmentation.  —  Count  the  human  radi- 
al pulse  during  four  consecutive  periods  of  fifteen 
seconds.  Let  the  subject  sip  cold  water  slowly. 
Eepeat  the  count  while  the  subject  swallows. 

The  frequency  will  be  increased. 

Variations  in  the  force  and  frequency  of  the 
heart-beat  follow  the  stimulation  of  most  afferent 
nerves,  for  example  the  central  end  of  the  divided 
vagus,  the  sciatic,  and  other  mixed  nerves,  the 
nerves  of  special  sense,  and  the  afferent  nerves 
which  arise  in  the  heart  and  pass  to  the  bulb. 

The  most  conspicuous  of  the  nerves  which  bear 
impulses  from  the  heart  to  the  central  nervous 
system  in  mammals  is  the  depressor.  This  nerve 
occurs  as  an  isolated  trunk  in  the  rabbit,  and  is 
found  mixed  with  other  fibres,  for  example  in  the 
vagus,  in  many  other  animals.  The  stimulation 
of  the  end  of  the  severed  depressor  nerve  in  con- 
nection with  the  heart  is  without  effect.  The 
stimulation  of  the  end  in  connection  with  the 
bulb  slows  the  heart  and  dilates  the  blood-vessels, 
thus  causing  a  great  fall  in  the  blood-pressure. 

The  Innervation  of  the   Blood-Vessels 

The  Bulbar  Centre.  —  1.  Lightly  etherize  a  large 
frog.  Expose  and  cut  both  vagus  nerves  (in 
order  to  exclude  inhibition  of  the  heart).  It  is 
of  the  first  importance  to  avoid  excessive  hemor- 


INNERVATION    OF    HEART    AND    BLOOD-VESSELS     569 

rhage.  Expose  the  brain  and  the  anterior  half  of 
the  spinal  cord  (page  565).  Place  the  frog  on  the 
web-board.  Note  carefully  the  speed  with  which 
the  corpuscles  pass  through  the  smaller  vessels 
of  the  web.  The  rate  of  flow  in  the  capillaries  is 
the  best  practical  index  .of  the  diameter  of  the 
small  arteries.  When  the  arteries  constrict,  the 
flow  in  the  capillaries  will  be  less  rapid.  Eemove 
the  cerebral  hemispheres  and  the  optic  lobes. 
After  five  minutes  or  more  (to  allow  the  frog  to 
recover  from  the  shock  of  the  operation),  note  the 
condition  of  the  web  vessels. 

There  will  be  no  significant  change. 

The  removal  of  the  brain  anterior  to  the  bulb 
has  not  destroyed  the  tonus  of  the  blood-vessels. 

Note  the  slow  rhythmic  changes  in  the  diam- 
eter of  the  vessels.  The  changes  are  not  uniform 
throughout  the  length  of  the  blood-vessel. 

2.  Curarize  the  frog  sufficiently  to  paralyze 
the  motor  nerves.  Stimulate  the  bulb  with  very 
weak  tetanizing  currents. 

The  flow  in  the  capillaries  will  be  less  rapid. 
Obviously  the  bulb  contains  nerve  cells,  the  ex- 
citation of  which  causes  the  narrowing  of  the 
blood-vessels.  These  cells  are  termed  the  bulbar 
vasoconstrictor  centre.  Eepeated  sections  show 
that  the  vasoconstrictor  cells  are  placed  (in  the 
rabbit)  on  both  sides  of  the   median  line  from 


570  THE    OUTGO   OF   ENEEGY 

about  one  millimetre  posterior  to  the  corpora 
qnadrigemina  to  a  point  about  four  millimetres 
posterior  to  those  bodies. 

The  Vasomotor  Functions  of  the  Spinal  Cord.  — 
1.  Divide  the  cord  just  posterior  to  the  bulb. 
(A  fresh  frog  may  be  required.  In  that  case, 
remember  to  curarize.) 

The  division  of  the  fibres  connecting  the  vaso- 
constrictor centre  with  the  cord  will  be  followed 
by  the  dilatation  of  the  vessels  in  the  web  (i.  e. 
the  flow  will  be  more  rapid). 

2.  Stimulate  the  peripheral  segment  of  the 
divided  cord. 

The  blood-vessels  will  constrict. 

Thus  the  neuraxons  (axis-cylinder  processes) 
of  the  bulbar  vasomotor  cells  pass  through  the 
spinal  cord  on  the  way  to  their  respective  blood- 
vessels. 

It  should  now  be  determined  whether  these 
fibres  pass  to  the  blood-vessels  without  interrup- 
tion, or  whether  they  end  in  contact  with  spinal 
vasomotor  cells  through  which  the  connection 
with  the  blood-vessels  is  made. 

3.  Wait  five  minutes  and  then  note  the  flow 
through  the  capillaries. 

The  dilatation  observed  immediately  after  the 
separation  of  the  cord  from  the  medulla  has  given 
place  to  moderate  constriction.     The  tonus  of  the 


INNERVATION    OF    HEART   AND    BLOOD-VESSELS    571 

blood-vessels  has  returned.  The  spinal  cord  has 
taken  up  the  vasomotor  function  of  the  bulb. 
Evidently  the  spinal  cord  contains  vasomotor 
cells,  which  ordinarily  are  subsidiary  to  those  of 
the  bulb,  but  which,  when  separated  from  their 
master  cells,  acquire^  the  power  of  independent 
action. 

Effect  of  Destruction  of  the  Spinal  Cord  on  the 
Distribution  of  the  Blood.  —  Further  evidence  of 
the  vasomotor  function  of  the  spinal  cord  is 
afforded  by  the  following  experiment. 

Expose  the  heart,  avoiding  unnecessary  loss  of 
blood.  Lay  bare  the  upper  part  of  the  intestine 
by  an  incision  on  the  left  side  of  the  umbilical 
vein,  which  lies  in  the  median  line.  Suspend  the 
frog  vertically.  Note  that  the  heart  and  the  great 
vessels  are  filled  with  blood.  Note  also  the  size 
and  number  of  the  vessels  in  the  walls  of  the 
stomach  and  intestines. 

Bend  the  frog's  head.  Put  the  seeker  into  the 
vertebral  canal  and  pass  it  gently  downwards  to 
destroy  the  spinal  cord.  The  seeker  will  move 
easily,  if  really  in  the  canal.  Look  at  the  heart 
and  great  arteries. 

The  heart  will  soon  be  bloodless,  though  beating 
regularly.  Examine  the  vessels  of  the  stomach 
and  intestine.  They  are  distended.  Evidently, 
the  contents  of  the  heart  and  the  great  arteries 


572  THE   OUTGO   OF   ENERGY 

have  passed  into  dilated  smaller  arteries  and 
veins.  It  would  be  found,  on  waiting,  that  this 
effect  is  not  a  passing  consequence  of  inhibition. 
The  destruction  of  the  spinal  cord  has  changed 
the  distribution  of  the  blood. 

The  Vasomotor  Fibres  leave  the  Cord  in  the 
Anterior  Roots  of  Spinal  Nerves.  —  1.  Eeniove 
the  arches  of  the  5th,  6th,  7th,  8th,  and  9th  ver- 
tebrae and  lay  bare  the  cord  in  a  large  frog  in 
which  the  motor  nerves  have  been  paralyzed  with 
curare.  Note  the  capillary  flow  in  the  web.  On 
the  side  on  which  the  web-vessels  are  examined, 
tie  a  silk  thread  around  each  of  the  anterior  roots 
near  their  origin  from  the  cord,  and  sever  the  roots 
between  the  ligature  and  the  cord. 

The  vessels  will  dilate. 

2.  Stimulate  the  peripheral  ends  of  several  of 
the  divided  roots. 

Constriction  will  follow. 

The  vascular  dilatation  which  follows  the  de- 
struction of  the  spinal  cord  is  not  permanent. 
After  a  time  the  vessels  regain  their  tonus.  It  is 
probable,  therefore,  that  vasomotor  nerve  cells 
exist  outside  the  spinal  cord,  and  this  conclusion 
is  confirmed  by  the  results  gained  on  warm-blooded 
animals  with  the  nicotine  method.  Langley  has 
found  that  the  injection  of  about  ten  milligrams 
of  nicotine  into  a  vein  of  a  cat  will  prevent,  for  a 


INNERVATION    OF   HEART   AND    BLOOD-VESSELS    5<3 

time,  the  passage  of  nerve  impulses  through  sym- 
pathetic cells.  Painting  the  ganglia  with  nicotine 
has  the  same  effect.  In  animals  the  sympathetic 
cells  of  which  have  thus  been  paralyzed,  the  stim- 
ulation of  the  lumbar  nerves  in  the  spinal  canal 
produces  no  change  in  the  vessels  of  the  genera- 
tive organs,  though  in  animals  not  poisoned  with 
nicotine  this  stimulation  causes  marked  constric- 
tion. The  lumbar  vasomotor  fibres  must  there- 
fore end  in  connection  with  sympathetic  nerve 
cells  which  transmit  the  constrictor  impulse  to 
the  blood-vessel.  Similar  observations  in  other 
regions  warrant  the  belief  that  all  the  vasomotor 
fibres  emerging  from  the  spinal  cord  end  in  like 
manner. 

Thus  the  vasoconstrictor  system  probably  con- 
sists of  three  neurons.  The  first  is  a  sympa- 
thetic cell,  lying  apart  from  the  central  nervous 
system.  Its  neuraxon  (axis-cylinder  process) 
passes  directly  to  the  blood-vessel.  The  second 
is  a  spinal  cell,  the  neuraxon  of  which  leaves  the 
cord  and  terminates  in  contact  with  the  sympa- 
thetic cell  or  its  branches.  The  third  has  its 
cell  body  in  the  bulb  and  its  neuraxon  termi- 
nates hi  contact  with  the  second  neuron. 

Commonly,  as  for  example  in  the  nerves  of  the 
extremities,  the  sympathetic  neuraxon  passes 
from  the  ganglion  along  the  gray  ramus  into  the 


574  THE    OUTGO    OF    ENERGY 

corresponding  spinal  nerve,  in  which  it  continues 
to  its  distribution. 

Vasoconstrictor  Fibres  in  the  Sciatic  Nerve.  — 
Curarize  a  frog  sufficiently  to  paralyze  the  volun- 
tary muscles  (any  excess  of  curare  will  paralyze 
the  vasomotor  fibres  also).  Carefully  destroy  the 
brain  with  the  seeker,  avoiding  loss  of  blood. 
Expose  the  right  sciatic  nerve  for  a  short  distance 
on  one  side,  using  the  greatest  care  not  to  injure 
the  blood-vessels.  Tie  a  thread  tightly  around 
the  nerve  near  the  upper  end  of  the  exposed  por- 
tion. Lay  the  frog,  back  upward,  on  the  web-board, 
placing  the  web  of  the  right  foot  over  the  notch, 
and  securing  it  with  fine  pins.  Examine  the  web 
under  a  low  power,  to  make  sure  that  the  circu- 
lation has  not  been  interrupted  by  stretching  the 
web.  Place  the  secondary  at  such  a  distance 
from  the  primary  coil  that  the  induced  current 
shall  be  barely  perceptible  to  the  tongue.  Set 
the  hammer  vibrating,  and  close  the  short-circuit- 
ing key.  Put  the  electrodes  under  the  sciatic 
nerve  on  the  peripheral  side  of  the  ligature.  Let 
a  second  observer  watch  a  small  vessel  of  the  web 
through  the  microscope.  Open  the  short-circuit- 
ing key  for  a  moment  only. 

The  blood-stream  slows  from  constriction  of 
the  supplying  vessels,  the  contraction  increasing 
during  a  few  seconds  and   then  subsiding. 


INNERVATION    OF    HEART   AND    BLOOD-VESSELS     575 

This  experiment  requires  much  care  and  close 
observation.  The  curare  effect  must  be  very 
slight ;  a  small  quantity  of  the  drug  should  be 
given  an  hour  before  the  observation  is  made. 
Great  pains  must  be  taken  to  use  feeble  currents 
and  not  to  prolong  the  excitation,  for  the  vaso- 
motor nerves  are  rapidly  exhausted.  The  nar- 
rowing of  the  arteries  of  the  web  is  usually 
evident  only  in  the  slowing  of  the  blood-stream 
during  excitation. 

Vasodilator  Nerves.  —  1.  Eepeat  the  preceding 
experiment  in  a  frog  in  which  the  sciatic  nerve  has 
been  four  days  severed  (without  injury  to  the  fem- 
oral vessels).  On  stimulation  of  the  peripheral 
segment  of  the  divided  sciatic  nerve,  the  vessels 
of  the  web  will  dilate  instead  of  constricting. 

Evidently  the  sciatic  nerve  contains  vasodilator 
as  well  as  vasoconstrictor  fibres.  When  the 
sciatic  fibres  are  separated  from  their  cells  of 
origin  by  the  section  of  the  nerve,  the  fibres  distal 
to  the  section  degenerate.  But  the  degeneration 
does  not  proceed  at  the  same  rate  in  all  the  fibres. 
The  vasoconstrictors  die  before  the  vasodilators. 
In  ordinary  stimulation  of  the  normal  nerve,  the 
action  of  the  constrictors  overpowers  that  of  the 
dilators.  In  the  partially  degenerated  nerve, 
the  same  stimulation  causes  dilatation  because 
the  constrictor  fibres  are  dead  or  dying. 


576  THE    OUTGO    OF   ENERGY 

2.  Note  the  rate  of  flow  in  the  web-vessels  in 
the  uninjured  limb.  Stimulate  the  sciatic  nerve 
with  the  single  induction  current  repeated  at 
intervals  of  five  seconds. 

The  vessels  of  the  web  will  dilate. 

The  vasoconstrictor  and  vasodilator  fibres  also 
react  differently  to  cold.  If  the  hind  limb  (cat) 
be  cooled,  the  stimulation  that  normally  causes 
vasoconstriction  will  cause  vasodilatation. 

Vasoconstrictor  and  vasodilator  fibres  are  not 
always  found  in  the  same  nerve-trunks ;  in  the 
chorda  tympani  nerve,  for  example,  there  are  only 
dilator  fibres. 

The  central  relations  of  the  dilator  nerves  have 
not  been  sufficiently  studied  to  warrant  their 
discussion  here. 

Reflex  Vasomotor  Actions.  —  1.  Note  the  rate 
of  flow  in  the  vessels  of  the  web  in  a  lightly 
curarized  frog.  Stimulate  the  skin  (not  too  near 
the  bulb  or  cord)  with  tetanizing  currents.  The 
stimulus  must  not  be  repeated  often,  or  fatigue 
will  obscure  the  result. 

Keflex  constriction  of  the  vessels  will  take  place. 
The  sensory  impulse  is  carried  by  afferent  fibres 
to  the  vasomotor  centres. 

Eepeat  the  experiment,  using  in  place  of  the 
electrical  a  mechanical  stimulus,  such  as  pinching 
the  skin  with  forceps. 


INNERVATION    OF    HEART   AND    BLOOD-VESSELS     577 


Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Inductorium.  Key.  Wires.  Dry  cell.  Electrodes. 
Needle  electrodes.  Frog-board.  Electromagnetic  signal. 
Heart-holder.  Kymograph.  Glass  tube  for  oesophagus. 
Two  muscle  levers.  Solutions  of  nicotine  (0.2  per  cent), 
atropine  (0.5  per  cent),  muscarine  (a  trace  in  normal  salt 
solution).  Curare.  Ether.  Sponge.  Glass  jar.  Ver- 
tebral saw.  Web-board.  Fine  pins.  Microscope.  Frog, 
the  sciatic  nerve  of  which  has  been  severed  four  days. 
Millimetre  rule.     Silk  thread. 


37 


INDEX 


Aberration,  chromatic,  432,  434  ;  diaphragm,  434 ;  spherical, 
by  reflection,  426  ;  spherical,  by  refraction,  427,  434. 

Absolute  force  of  muscle,  358. 

Accommodation,  469 ;  angle  between  light  and  visual  axis, 
487  ;  far  point,  479  ;  iris,  474  ;  lens,  474,  475,  477  ;  liue,  472 ; 
measurements,  479  ;  mechanism,  473  ;  pupil,  473  ;  pupil,  near- 
ness, 488  ;  pupil,  size,  488  ;  range,  471,  484. 

Acuteness  of  vision,  465,  466. 

Action  current,  brain  and  cord,  319;  decrement,  309;  dura- 
tion, 314;  glands,  320;  heart,  310,  312;  threshold  value, 
318;  human  muscle,  309;  muscle,  300;  nerve,  315;  optic 
nerve,  318;  positive  after  current,  317;  positive  variation, 
316;  precedes  change  in  form,  311;  tetanus,  305;  voltage, 
315. 

Afferent  impulses,  reflex  action,  371 ;  summation,  372. 

Alteration  hypothesis  of  nerve  and  muscle  current,  299. 

Amalgamation,  46 

Ametropia,  determination  of,  493. 

Angle,  construction  of  tangent,  467  ;  incidence,  403  ;  reflection, 
403  ;  refraction,  411 ;  sine,  414  ;  visual,  464. 

Angle  gamma,  464. 

Animal  heat,  285. 

Ankle  jerk,  376. 

Anodes  and  cathodes,  physiological,  110. 

Anterior  roots,  vasomotor  fibres,  572. 

Aortic  regurgitation,  550. 

Aortic  stenosis,  551. 

Aperture,  420,  427. 

Apparatus,  criticism  of,  84. 

Arrhenius,  theory  of  dissociation,  31. 

Artificial  scheme,  511. 

Astigmatism,  464 ;  measurement,  495. 

Atropine,  action  on  heart,  564. 

Augmentor  centre,  566. 

Axis,  optical,  419 ;  optical,  eye,  439  ;  principal,  419  ;  visual  463. 


5S0  INDEX 

Balancing  experiment,  379. 

Bernstein's  experiment,  531  ;  rheotome,  313. 

Blood  pressure,  arterial  in  frog,  522 ;  influenced  by  inhibition, 

525  ;  peripheral  resistance,  523. 
Blood-vessels,  innervation,  568. 
Brain  of  frog,  565. 
Brain,  destruction  by  pithing,  97 ;  dorsal  view,  293. 

Calcium,  in  normal  solution,  165. 

Calorimeter,  Rubner's  experiment,  285. 

Carbon  dioxide,  action  on  nerve,  172;  apparatus,  173. 

Caustic  surface,  427-429. 

Cell,  dry,  52  :  Daniell,  48 ;  galvanic,  34. 

Cell,  in  series,  133. 

Centre,  rotation,  463  ;  optical,  420  ;  optical,  crystalline  lens,  446. 

Centres  of  heart  nerves,  564. 

Cerebral  hemispheres,  removal  of,  378. 

Chemical  stimulation,  163. 

Circle,  dispersion,  429,  470-472. 

Circulation,  artificial  scheme,  511;  capillary,  262,  569;  inter- 
mittent and  continuous,  515  ;  mechanics  of ,  508  ;  mesentery, 
519  ;  rate  of  flow  and  width  of  bed,  519. 

Clamp,  double,  65 ;  flat-jawed,  65 ;  Gaskell,  103 ;  round-jawed, 
65. 

Clausius,  theory  of  dissociation,  29. 

Closing  contraction,  98. 

Color  blindness,  501. 

Compensation  of  demarcation  current,  294. 

Compensatory  pause,  533. 

Conductivity,  168;  centripetal  and  centrifugal,  181;  during 
constant  current,  123. 

Contraction,  tonic,  141. 

Contraction,  direction  of  current,  157;  human  muscle,  353; 
idiomuscular,  166;  law,  113;  load,  341  ;  opening  and  closing, 
98  ;  rhythms,  142  ;  single,  332  ;  temperature,  342  ;  torn".,  107, 
140;  veratrine,  345  ;  wave,  338  ;  heart  muscle,  534. 

Contracture,  340. 

Coordinated  actions,  378. 

Croak  reflex,  379. 

Curare,  97  ;  poisons  end  plates,  171. 

Daniell  cell,  48. 

Decrement  of  action  current,  309.  » 

Demarcation  current,  287,  295 ;  hypotheses,  297 ;  interferes 
with  stimulating  current,  292  ;  measurement,  292  ;  muscle, 
287  ;  negative  variation,  305  ;  nerve,  296;  stimulus,  289,  296. 

Dennett's  method,  numbering  prisms,  435. 


INDEX  581 


Depressor  nerve,  568. 

Deviation,  angular,  435. 

Dicrotic  notch,  545. 

Diffusion  of  gases,  14. 

Dioptre,  435.' 

Dispersion  circle,  429,  470,  471,  472. 

Distance,   focal,  crystalline  leus,  450 ;   principal  focal,  cornea, 

441. 
Distilled  water,  a  chemical  stimulus,  163. 
Drying,  149,  164. 

DuBois-Reymond,  molecular  theory,  298. 
Duchenne's  points,  127. 
Duration  of  stimulus,  138. 

Elasticity  and  extensibility,  of  a  metal  spring,  364  ;  of  a  rub- 
ber band,  364  ;  of  skeletal  muscle,  365. 

Electric  fish,  329. 

Electrical  units,  35. 

Electrodes,  for  human  nerves,  132 ;  indifferent,  111 ;  non-polariz- 
able,  93  ;  platinum,  65. 

Electrolysis,  26. 

Electrolytic  solution  pressure,  32. 

Electrometer,  34. 

Electromotive  force,  34,  287 ;  demarcation  current,  292. 

Electrotonic  currents,  323 ;  as  stimulus,  328  ;  negative  and 
positive  variation,  325  ;  polarization  increment,  325. 

Energy,  set  free  in  various  forms.  10 ;  stimulation,  and  irrita- 
bility, 7  ;     developing,  361. 

Emmetropia,  490;  angle  of,1 464. 

Engelmann's  incisions,  534. 

Ergograph,  354. 

Excitation  wave,  336  :  remains  in  original  fibre,  181. 

Extensibility,  364,  366. 

Extra  contraction  of  heart,  533. 

Eye,  artificial,  ophthalmoscopic,  489 ;  as  camera  obscura,  437 ; 
normal  measurements,  461  ;  see  optical  box,  404 ;  reduced, 
458  ;  schematic,  438. 

Extra  current  in  inductorium,  68. 

Fatigue,  367  ;  human  muscle,  368  ;  polar,  147. 

Fixation,  line,  463. 

Focus,  conjugate,  concave  mirror,  427  ;  conjugate,  convex  lens 
418  ;  conjugate,  cornea,  444  ;  principal,  concave  mirror,  405 
principal,  construction,  443;  principal,  convex  lens,  416 
principal,  eye,  454. 

Focal  distance,  concave  mirror,  406  ;  principal,  convex  lens,  417 

Focal  line,  427. 


582  INDEX 

Food  materials,  composition  of,  281. 

Flexors  and  extensors,  relative  excitability,  177. 

Frog  board,  112. 

Galvanic  cells,  electromotive  force  in,  34. 

Galvanic  stimulation  may  cause  periodic  impulses,  144. 

Galvanotropism,  137. 

Gas  chamber,  173. 

Gaskell's  block,  535  ;  clamp,  103. 

Goltz's  experiment,  567. 

Gower's  experiment,  376. 

Graphic  method,  77. 

Heart,  action  current,  310,  312  ;  apex,  isolated,  531 ;  atropine, 
564 ;  augmentor  centre,  566  ;  augmentor  nerves,  555 ;  auric- 
ulo-ventricular  interval,  561  ;  Bernstein's  experiment,  531  ; 
calcium,  539  ;  change  in  form,  529 ;  chemical  theory,  540 ; 
compensatory  pause,  533  ;  constant  stimulus,  532 ;  contrac- 
tion curve,  530 ;  contraction  wave,  534  ;  excitation  from  auri- 
cle to  ventricle,  535;  exposure,  112;  extra  contraction, 
533 ;  Gaskell's  block,  535 ;  graphic  record,  530 ;  impulse, 
541 ;  inhibited,  559 ;  inhibitory  centre,  564  ;  inhibitory  mech- 
anism, 562  ;  inorganic  salts,  538  ;  irregularities,  536  ;  irritable 
though  inactive,  533;  irritable  though  inhibited,  561  ;  load, 
537  ;  maximal  contraction,  530;  monopolar  stimulation,  111  ; 
muscarine,  564;  nerve-free,  170;  nicotine,  563;  outflow 
period,  526;  polar  inhibition,  153;  polar  stimulation,  110; 
potassium,  539 ;  pump,  525  ;  reflex  augmentation,  568 ;  re- 
flex inhibition,  567  ;  refractory  period,  533  ;  rhythmic  con- 
tractility, 532  ;  sounds,  541  ;  staircase  contraction,  531  ;  tonus, 
537  ;  Stannius  inhibition,  562  ;  sympathetic,  556 ;  tempera- 
ture, 538;  vagus,  559;  valves,  511,  525,  550,  551,  552. 

Heat  values,  calculation,  285. 

Hypermetropia,  431 ;  angle  of,  464  ;  measurement,  495. 

Idio-muscular  contraction,  166. 

Image,  concave  mirror,  405,  409  ;  convex  mirror,  410  ;  convex 
lens,  419,  420;  cornea,  443;  dioptric,  456,  457  ;  retinal,  437,; 
retinal,  actual  size,  465;  retinal,  apparent  size,  464;  smallest 
perceptible,  466;  virtual,  concave  mirror,  408;  virtual,  con- 
cave lens,  419. 

Index  of  refraction,  412. 

Induction  currents,  54  ;  direction,  158  ;  gap  in  resulting  contrac- 
tions, 161;  magnetic,  56,  58;  nerves,  69  ;  stimulus,  66,  158; 
unipolar,  71. 

Inductoiium,  54;  construction,  60;  graduation,  83. 


INDEX  583 

Inhibition,  galvanic,  153;  heart,  559;  polar,  155 ;  reflex  of 
heart,  567  ;  ventricular,  524. 

Inhibitory  nerves  of  heart,  558. 

Inhibitory  centre,  564. 

Interrupter,  62,  303. 

Ions,  28. 

Iris,  accommodation,  474. 

Irritability,  169  ;  definition,  9  ;  different  points  of  same  nerve, 
180;  flexor  and  extensor  nerves,  177;  muscle,  independent, 
169  ;  nerve  greater  than  muscle,  179  ;  separable  from  conduc- 
tivity, 172. 

Isometric  contraction,  352,  355  ;  method,  349. 

Isotonic  method,  349. 

Isotony,  20. 

Key,  short-circuiting,  46  ;  simple,  45  ;  rocking,  50. 

Kinetic  theory,  12. 

Knee  jerk,  375. 

Kymograph,  79;  long  paper,  81. 

Lantern,  404. 

Latent  period  of  muscle,  334. 

Lens,  accommodation,  474,  475;  concave,  422;   convex,  416; 

numbering,  435. 
Lever,  light  muscle,  86  ;  heavy  or  rigid,  351 ;  writing,  87. 
Light,  spectrum,  413. 

Line  of  fixation,  463  ;  focal,  427  ;  force,  57. 
Load,  influence  on  contraction,  537. 

Magnetic  field,  57  ;  induction,  57. 

Make  or  break  current  excluded,  70;  stimuli,  67. 

Manometer,  mercury,  523. 

Mechanical  stimulation,  166. 

Mirror,  concave,  405  ;  convex,  410  ;  plane,  403. 

Mitral  incompetence,  552. 

Moist  chamber,  95. 

Molecular  hypothesis  of  nerve  and  muscle  current,  298. 

Monopolar  stimulation,  111. 

Motor  points,  128. 

Muscarine,  action  on  heart,  564. 

Muscle,  action  current,  300 ;  clamp,  8 ;  curve,  333 ;  demarca- 
tion current,  287  ;  form  affects  stimulation,  156  ;  left  hind 
limb  of  frog,  6,  99;  lever,  86,  351 ;  tonus,  389;  turbid  and 
clear,  335  ;  warmer,  343. 

Myomeres,  298. 

Myopia,  430  ;  angle  of,  464 ;  measurement,  493. 


584  INDEX 

Negative  variation,  321  ;  electrotonic  currents,  325  ;  secretion 
currents,  321. 

Nerve,  action  current,  315  ;  cervical  in  frog,  558  ;  conducts  in 
both   directions,    181;   conductivity,    120;   conductivity  and 
irritability,    172 ;    demarcation   current,    295 ;   drying,    149 
electrical   resistance,   327 ;    electromotive   phenomena,  295 
impulse,    speed   of,    184 ;    induction,    69 ;    inhibitory,    558 
irritability,  116;   irritability   compared   with   muscle,    179 
irritability,  different  points,  180;   irritability,  specific,  179 
polarization,  323;  polar  stimulation,  113,  131  ;  stimulated  by 
own  demarcation  current,  296. 

Nerve-muscle  preparation,  4. 

Nicotine,  action  on  heart,  563. 

Nitrite  of  amyl,  550. 

Normal  saline  solution,  165. 

Ophthalmoscope,  489. 

Ophthalmoscopy,  484 ;  direct,  490 ;  indirect,  496. 
Optic  nerve,  action  current,  318. 
Optical  box,  404. 

Opening  and  closing  contraction,  98,  125  ;  tetanus,  147. 
Ordinates,  91. 
Osmometer,  18. 

Osmotic  pressure,  16;  blood-corpuscle  method,  22;  blood 
serum,  21. 

Paper,  smoked,  method  of  usiug,  78. 

Paradoxical  contraction,  328. 

Paramecium,  galvanotropism,  137. 

Partial  pressure,  13. 

Periodic  contraction  from  chemical  stimulation,  165  ;  galvanic 
stimulation,  144. 

Peripheral  resistance,  521. 

Permeability,  24. 

Pithing,  97. 

I'lasmolysis,  20. 

Plethysmograph,  545. 

Point,  cardinal,  cornea,  440;  cardinal,  crystalline  lens,  445; 
cardinal,  eye,  439,  451  ;  far,  accommodation,  479 ;  far,  deter- 
mination, 479  ;  near,  accommodation,  480 ;  near,  determina- 
tion, 480;  nodal,  420;  nodal,  crystalline  lens,  447;  nodal, 
eye,  453  ;  principal,  crystalline  lens,  450  ;  s,  449,  453. 

Polar  excitation,  148;  fatigue,  147;  inhibition,  153,  155;  in- 
jured muscle,  151  ;  refusal,  292;  stimulation,  101,  113,  159. 

Polarization,  46;  current,  51,  145;  increment,  325;  positive 
variation,   146. 

Pole-changer,  49,  50. 


INDEX  585 

Positive  after  current,  317. 

Positive  variation,  action  current,  316  ;  polarization  current, 
146  ;  polarizing  current,  325. 

Prentice's  method,  numbering  prisms,  435. 

Prisms,  413;  construction,  413;  numbering,  435;  path  of  en- 
tering ray,  413. 

Pulse,  aortic  regurgitation,  550 ;  curve,  546 ;  dicrotic,  545 ; 
form,  544 ;  frequency,  543  ;  hardness,  544  ;  low  tension,  549  ; 
pressure,  545;  valvular  disorders,  551,  552;  volume,  545, 
552. 

Pupil,  accommodation,  473. 

Reaction  of  degeneration,  135. 

Reaction  time,  382. 

Reflection,  concave  mirror,  405;  convex  mirror,  410;  plane 
mirror,  403. 

Reflex  actions,  370 ;  afferent  impulses,  371 ;  cornea,  374  ;  inhi- 
bition, 384  ;  man,  374 ;  pupil,  375  ;  purpose,  381  ;  segmen- 
tal, 373 ;  strychnine,  377  ;  tendon,  375  ;  threshold,  372 ; 
throat,  382  ;   vasomotor,  576. 

Reflex  time,  382. 

Refraction,  410;  concave  lens,  422 ;  convex  lens,  416;  convex 
and  cylindrical  lenses,  combined,  424  ;  cylinders,  422  ;  eye, 
437 ;   index,  412  ;   prism,  413. 

Refractory  period,  534. 

Respiration,  mechanics  of,  505. 

Respiration  scheme,  505. 

Retina,  reflection,  484. 

Rheochord,  42. 

Rheoscopic  frog,  302,  306. 

Rheotachy  graph,  Hermann,  314. 

Rheotome,  differential,  Bernstein,  313. 

Ringer  solution,  540. 

Ritter-Rollett  phenomenon,  177. 

Salts,  influence  on  contraction  of  heart,  538. 

Saturation,  16. 

Scheiner's  experiment,  469. 

Sciatic  nerve,  vasomotor  fibres,  574. 

Secretion  current,  320;  negative  variation,  321. 

Semi-permeable  membrane,  17. 

Shortening  in  single  contraction  and  in  tetanus,  348. 

Sensation,  effort,  400;  general,  398;  irradiation,  398;  motion, 
400 ;  motor,  400 ;  pain,  399 ;  pressure,  393  ;  taste,  401  ;  tem- 
perature, 390  ;  tickle,  398 ;  touch,  395  ;  Weber's  law,  395. 

Signal,  electro-magnet,  105. 

Size,  apparent,  456, 465. 


586  INDEX 

Skin,  hot  and  cold  spots,  390;  irradiation,  398;  pressure  spots, 
393. 

Smooth  muscle,  356. 

Solution,  gas  in  liquid,  16;  normal,  165;  solid  in  liquid,  16; 
tension,  16. 

Spectrum,  413,  432. 

Sphygmograph,  527. 

Spinal  cord,  localization  of  movements  at  different  levels,  387  ; 
destruction  changes  distribution  of  blood,  571. 

Spinal  nerve  roots,  386  ;  sensory  nerves,  388. 

Spontaneous  contractions,  356. 

Staircase  contraction,  heart,  531. 

Stannius  ligature,  562. 

Stimulation,  9  ;  angle  of  current  lines,  157  ;  chemical,  163,  164  ; 
constant,  may  cause  periodic  contraction,  165 ;  demarcation 
current,  290,  296;  distilled  water,  163;  drying,  164;  form 
of  muscle,  10,  156;  induction  current,  158;  intensity  changes, 
99;  mechanical,  166;  minimal  and  maximal,  175;  monopo- 
lar, 111;  polar,  in  heart,  110;  summation  of  impulses,  176; 
threshold  value,  174;  unipolar,  errors,  320. 

Stroboscopic  method,  305. 

Surface,  caustic,  427,  428,  429 ;  principal,  crystalline  lens, 
418  ;  principal,  eye,  449. 

Surface  tension,  25,  36. 

Summation  of  stimuli,  176. 

Superposition  in  tetanus,  347. 

Superposition  of  two  contractions,  346. 

Sympathetic,  action  on  heart,  556 ;  frog,  556 ;  preparation, 
555. 

Synchronous  poiuts,  method  of  obtaining,  120. 

System  A,  schematic  eye,  440 ;  B,  schematic  eye,  445 ;  C, 
schematic  eye,  451. 

Temperature,  hourly  variation,  285  ;  mouth,  affected  by  food, 
285;  reaction  to  variations  in,  285  ;  regional,  285. 

Tension  indicator,  25. 

Tetanus,  69,  346  ;  electrical  phenomena,  305  ;  natural  and  arti- 
ficial, 355  ;  opening  and  closing,  147  ;  Ritter's,  149. 

Threshold  value  of  stimulation,  175. 

Tonus  of  heart  muscle,  537. 

Tradescantia  discolor,  20. 

Tuning  fork,  88. 

Unipolar  induction,  71,  stimulation,  errors,  320. 

Van  I'll:  \V.\ai.'>  hypothesis,  14. 
Van't  Iloff's  discoveries,  20. 


INDEX  587 

Vagus,  preparation,    558;   inhibits  heart-beat,  etc.,   559,  560, 

561. 
Vapor  pressure,  15. 
Vasodilator  nerves,  575. 
Vasomotor  centre,  570  ;  fibres  in  anterior  roots,  572  ;  functions 

of  cord,  570  ;  reflexes,  576  ;  sciatic,  574. 
Veratrine,  influence  on  contraction,  345. 
Vision,  acuteness,  465,  466  ;  blind  spot,  499  ;  color  blindness, 

501  ;  field  of,  500;  yellow  spot,  499, 
Volume  of  contracting  muscle,  331. 
Volume  tube,  332. 

Wohler's  discovery,  3. 

"Work  adder,  359. 

"Work  done,  influenced  by  load,  35S. 


—  ~T  ^r  ^  A  — #- 


JUN  2  6   1928 


-    r   ... 


